Intriguing question. I have no idea what (if any) limits there are, as I have never pushed things that far.
My guess would be that memory is the only limitation. All links in SM are nothing more than references to memory locations where the data is kept (equivalent to a float variable in code). Whether they are wireless, bussed etc. is little more than a choice of how we would like the data presented graphically - and I see no reason that bus/wireless names should be any more greedy than any other text annotation that we put in our schematics.
In a way, links (of any sort) don't really exist inside SM - once securely "hooked up", all that happens is that output connectors dump their data in a certain memory location, and inputs fetch that data whenever they need it. Apart from triggers, there isn't any coded "mechanism" involved in passing the data. The links we see inside the workspace are not "conduits" or "pipes" along which things truly flow - they are just a graphical representation of which connectors reference the same "variable".
AFAIK, the only penalty for using wireless or busses is a tiny bit of text parsing that happens at the moment of making a connection - no different really than what must happen when we use the mouse to drop a link onto a connector. In fact there is an interesting contrast between busses and selectors/multiplexers in this respect...
Once a bus is connected, that's it, the ends are joined and it is "invisible" until you next make a change. In contrast, with multiplexers and selectors, a green trigger at any input, causes the index to be polled - sometimes resulting in quite a flurry of triggers while SM goes about "double-checking" the routing.
So busses should in theory handle "green" data more economically than a selector/multiplexer routing matrix - the downside is that busses have a lot more to do when changing presets etc. (parsing the connector names).
AFAIK, it is still not possible to "nest" busses - that is, you can't use a "sub-bus" as an input to a Bus Create.
However, one thing you can do is to "sum" the outputs of several Bus Creates. If you do this, the combined bus will contain all of the unique "links" from all the "added" buses. If any buses have links of the same name, the combined bus will have one link of that name, and the various inputs will be summed...
Feel free to use any schematics and algorithms I post on the forum in your own designs - a credit is appreciated (but not a requirement).
Don't stagnate, mutate to create. Without randomness and serendipity the earth would be just another barren rock.