I’m unfamiliar with boa but it might make sense in some scenarios to split up snaps, ScummVM could potentially have had a second snap containing the extra assets and declared a content sharing interface allowing you to split apart the two and potentially just not have the demos, of course the content snaps would end up having revision history so it probably doesn’t make sense for Boa if space alone is the concern.
I think aside from waiting for other compression options with better compression ratios, the most obvious choice it to download the assets distributed outside the snaps filesystem itself, but this comes with the problems of hosting, more complex setup procedure, keeping the assets updated seperately to the snap itself, etc.
I just took a look at the steam stats, 1.16% of Steam users have less than 10GB available, although I’m unsure if this is counted across every drive or simply the OS’ primary drive which makes this fairly ambiguous (It’s not too uncommon for people to have a faster SSD for critical apps and slower SSD’s or harddrives for things like games, and I don’t think snap makes it trivial to decide which drive snap files are stored in so this could be a big factor here).
I see your point of different expectations in the software center vs a client like Steam itself, but the software center is never particularly straight forward when people might have different download sizes on the orders of several hundred MB over shared dependencies. A snap has an an absolute calculated size on the harddrive shown in in the software center as size of the snap itself minus its base/extensions/etc, whereas a small 10KB Java game might be a 100MB Java game overall if the user doesn’t use Java otherwise. In that sense the snap is more truthful, so I’m unsure the software center is amazing for reporting disk space usage in general.
Edit: When filtering the steam stats to Linux only, there’s 7% of the userbase with less than 10GB available. This does begin to seem more concerning but it’s still ambiguous how the stats are counted (multiple drives particularly, given how Linux systems tend to use multiple partitions mounted under the common / directory).