You can easily define an "all" category, just check the category-settings
Random Category is nice idea, maybe that is something I can quickly build in
Mutliplayer-Gaming is supported via PNflashgames, but they recently stopped their Multiplayer-Games, I am waiting for this to come back.
If there are multiplayer-Games in a "new format" available we will try to implement them, too. There is even some plan to extend the list of compatible Games to other Arcade-Systems ...
Just wait for ibProArcade v2.5.5+ which is about to come *whistle*