If we are guessing numbers, 1100 seats is as logical as 500. Based on the fact that the other GA+ was 650 seats to 300 bar capacity.
All we know is that there will be a new 500 capacity bar offering in the City Hall. How many seats are associated with that or what it does to the overall City Hall capacity and use, or how or if it affects the original GA+ in the stand, whether it even IS a version of GA+, we just have no idea at this point.
That btw isn't so much aimed at you, but for the benefit of others that may take the 500 mentioned in a few posts as fact.