If I understand properly, the idea behind the change in the booking system was to reduce the strain on the Estrel Staff (and sadly it had the opposite effect).
Instead, to even out the stress on the system and to reduce frustration for all parties involved, how about adopting a system similar to how big planes are boarded?
The way it happens, is that seating opens up by row ranges - e.g. passengers with seat rows 70-99, then 50-99, then 30-99, etc. - as a way to control the boarding flow.
Applied to hotel booking, the basic idea would be:
1) Registration opens on day X
2) On day X+7, hotel booking opens for registrars with ID 1-400
3) On day X+14, hotel booking opens for registrars with ID 1-800
4) On day X+21, hotel booking opens for registrars with ID 1-1200
etc.
That way:
1) The registration system itself acts as a "queuing system" by re-using your registration ID as your hotel booking ticket number;
2) The stress is evened-out in a way that is known in advance both for registrars and the Estrel Staff;
3) It requires pre-planning (do we open up for 400 registrars at a time, or more, or less? Do we leave 7 days between openings, or more, or less?), but once that is done, it requires minimal efforts to maintain once running - just cross-checking the registration ID with (1) the planning (is booking open for that ID range?) and (2) the registration details (to avoid people saying "I have ID 244, book me a room" whereas they actually have ID 2440).