This is probably just selectively enabling /AS and /DS to individual slots based on the status of a physical/logical switch to enable/disable.
I would be curious what U1 is doing - perhaps allows for installation of an accelerator in a certain one of the slots - but I don't expect anything terribly exotic. Termination resistors to help with signal integrity, pulls, buffer caps. It's not going to allow running multiple cards at the same time, just a way to switch between them. But as long as cards are well behaved, if you don't show a disabled card the address and data strobes disabled cards could happily co-exist on the same bus. Just don't change the status of the switch without the system being in reset (or powered off).