Ok, so this is really becoming a bit... let's say tedious.
I'll make 2 parts, the first is roughly 2/3 of the post, if you're tired of the ongoing discussion, skip ahead to the other points further down.
We got the following points down:
DD items are often sold out - for specific artists - when normal attendees are able to get in. Ok, that's a given, and it wouldn't change even without any Sponsors at all. Some are high in demand, without those respective lines you need to camp hours before opening, missing out on events (as I said already) and leading to blocking the passages (as I said already). The size and order of arguments is non-important in that matter, it was said, don't throw it on the side, no matter how much emphasis was given towards it.
Solutions:
Ask the respective artist before the opening of the Dealers Den, some will say no, some will gladly give the respective item away beforehand, just simple business after all.
Ask a friend with a Supersonsor to reserve a slot, if you don't know anyone... well, get the Supersonsor yourself if you just can't live without the respective item in mind.
Ask the artist outside of a con for a commission, yes, not every artist offers those, but many do.
With those 3 in combination, receiving the respective item should be doable. There respective amount of people not able to work with even one of those 3 solutions is particularly small, so sadly to say - they don't matter in the big picture. If you're one of those people, well... that's as sadly to say tough luck, and surely possible to get yourself into the position to use one of those solutions with a bit of effort.
Also, as a fourth option: Propose a commission with triple payment up-front to the respective artist, many will gladly 'open' a spot in their list. If you really want something, there is always a way.
Next thing: Unfairness. If you want to speak about that, don't disregard any particular point about it because of your personal views. ANY perk at all is unfair, that's why it's... well... a perk. Nobody will even care if you pay the Supersonsor or normal attendee if you're blatantly stating "I'll only do it IF!', this line of reasoning is useless. Either you like the con enough to pay the extra price, or you don't, nothing more, nothing less. Everything else is a bonus, was always intended like this, and is mostly handled like this as well, with beneficial side-effects that can't be overlooked.
So, given this, I'm also quite curious as to which items you might refer to, or rather the artists in respect which are usually sold out by the time the normal attendees have entrance. If it was a special item, I'm sure with a personal talk many things can be handled. If they were not merch but individual things... well, those are rare in itself, and the only obvious one are commissions of any sort, leading us back to those said solutions. If the artist is out of materials to provide any service you absolutely want, and just can't afford not to have for your mental well-being... suggest going out and getting said materials for them, I'm sure the respective artist is fairly happy about that, and Berlin is a nice and big town with everything available in the course of a single day.
If you got a solution, then please present it, don't just say 'stop this, it's unfair!'. Yes... life is unfair, deal with it. If you want to make it better, provide solutions to make it such, if someone smashes it to smithereens because it involves massive problems accounted to the idea, make it better until it's a viable solution. If it's shut down then... well, then and only then you got the right to complain.
As for artists being out in general: Not everyone will EVER be able to get a picture of the 'famous' artists. Either because their price-range is out of reach, or the slots are always closed, or any other reason. Just because other people get access at different times, the same amount will still receive something from them. So, the bigger question for me is who to give them to rather. Normal attendees or any sort of Sponsor? I would say the later, simply because they keep the convention running to a large degree. Quite a large amount of artists are freelancers without any knowledge about running a proper business either, so they don't know when to raise the price, or how to price from the beginning, which leads to said 'cheap but never available' artists.
But away from that now, I'll speak about the other parts of your initial post then:
Water availability:
That's actually quite a hefty problem at Estrel, as a single bottle of water from their hotel costs 8€, which is... well... sorry to use the term, but that price is simply appalling. There ought to be a simple way to receive clean, fresh and simple tap-water, nothing fancy or out of the norm, just fluid to live by, that's true.
I suggest talking about water-dispensers with degradable cups, they are cheap to rent and can be set up in minutes. Just the allowance from the hotel needs to be there. And if they don't allow it, it would be a good thing for their business, but a bad thing for their reputation definitely. Nobody likes people falling down from dehydration, and we have far too many each year anyway. That would alleviate the problem slightly. If it can't be done out of safety concerns of any way... well, then that's a shame.
Feedback session:
I frankly wasn't there, missed the timespot, so I can't speak much about it. What I suggest is a separate panel if time allows for it, with some of the people in higher positions being there to receive the feedback related to their posts. It would make it easier to get the lines sorted out if it becomes a common thing, as well as better the con with out-of-the-box thinking.
Main bar:
I mainly got my things there, this year they were quicker then before. Not perfect, sometimes they worked literally at snails pace, focusing on shifting around things rather then actually selling stuff, but that's the common thing we got used to. It's not bad, it's not perfect, but it's fine for the mass of people. They need to work on a better system to get the most wanted things out swiftly though.
Length of the PPS:
It's fine, therefore 3 segments. Just Cheetah needs to allow other ideas then his own to be done. One good way to achieve this would be a little price-event, drafts are sent in after the topic for the next con is revealed and the best draft wins a little price... and becomes next years paw-pet-show. It would keep the quality of the show up sky-high, as well as solve those problems with clear overworking and time limitations for thinking up new stories over and over again. It's a great show, it's had great years, but the same problems arise regularly, especially with evaluating what's a quality story and what isn't. The team makes a massive effort, but it simply feels like there isn't put enough effort - or simply not the most efficient effort rather said - into proof reading and plugging plot-holes.
As a few of those things which shouldn't happen but have:
The main character not progressing emotionally during the play.
Side characters are the actual main characters.
The 'villain' side is abstracted and not properly worked out.
Changes in characters from one scene to another are sometimes not explained at all.
That's why EF 14 and 23 were such good shows remembered by many. Those parts were all clear set, it was emotional and understandable for most people, and the time wasn't any concern. If those things can be made as good as the acting, the preparation of the puppets and the work put into effects then every year would be as memorable. Though.. it's also the hardest part to get right, and even seasoned story readers and writers miss out on crucial things from time to time, it would simply lower the chances of such things to happen.
