During todays hackday here at the office, I decided to take a look at the previous restriction of only being able to have 16384 sprites per collection. It was due to another optimization regarding index buffers that we got the new behavior. However, that check can be dynamic in the engine, so I tested this today, and it works fine. This allows for a user specified number larger than 16384. Note that the maximum number of gameobjects per collection is still 32767!
Here is another example, using the vanilla engine (1.2.127) where I create 16000 bunnies in each collection, and thus push the limits some more. The current threshold on my iMAC is ~50000 bunnies for 60fps, after that it starts to drop:
My code should be cleaned up, and I also need to talk to @britzl on the subject of supporting it for all the cases in the Bunnymark test.