Oh. This makes things harder. This topic was meant to be about saving server space, but I can see that that isn't the main problem. You have to decide on a policy however. Eventually, google apps script will support websockets, and clever use of firebase could create cloud variables. Banning this type of thing is possible (not in snap, but just by making it not permitted) and so are cloud messages, (or variables) but leaving it as possible iff you run your own server or use firebase (with much more limited free plan) does not seem fair.
On some other topic, you said that a way to make cloud variables would be to use google sheets. However, their API could change. Google apps script would essentially be the same. It acts like an https? server that has access to your google drive. Combining that (or any other server like the German snap!chat server) with messages (from Snap! itself or elsewhere) would be full cloud variables, which is what I actually want.
Why do I keep reading snap!chat as an email address?