The World SF convention started in 1939. In the past 73 years, it seems no-one has realised that it’s difficult for mobility impaired members to get to panels or that they might need a little extra space. (When I wrote this post I linked to an article complaining about lack of disability access but it’s gone now.)
If the elevators are so crowded that wheelies (mobility impaired people using scooters or chairs) can’t get in them, then I suggest that walkies wait, encouraging them to walk up the bloody stairs! Apparently no-one has suggested having areas set aside for mobility impaired people who might arrive late due to difficulties navigating crowded corridors. Of course, there’s no precedent in the real world for provision of disability access in this way.