Hey there Jono the guy has loads of plans for what he wants to do in the future, off the top of my head and to address your suggestions.
* Other players coming and going and playing machines
He's already working on online integration, so that you can visit other people's arcades and play their machines, currently everyone gets the same arcade, but the idea is (probably still a way off though!) that you can download other arcades with their own selection of machines, not knowing what state they're in, and all that sort of thing. I can't say this will extend to having actual human character models walking around and stuff (there's been no mention of that), but he definitely wants to take it in the direction of online sharing of arcades and machines.
* Doors to the 'outside world along one of the exterior walls with people going past, some coming into the arcade.
*Staff offering drinks and change, even challenging the odd punter to leave as they're under 18 (awesome RG stance in today's climate)
I'll deal with these together, yes there are plans to make the arcade more visually involving and complete, but of course every new addition to the arcade has to be designed by hand, 3D modelled, rendered, tested etc and then added in, and currently this guy is doing it all by himself in his spare time as a hobby!
* Centralised change desk (like we see in seaside type arcades)
See above, this has been talked about already, but it's a question of getting it modelled and built, which takes time
* Some form of decoration on the walls, promotional posters for example
If you take a look at my latest video you'll see he's currently working on getting the correct cabinet decals on the cabinets, which is a slightly different thing but in the same ballpark. Overall this whole project is very early days, the guy has loads of plans with what he can do to make it better and more like a real arcade