One question I wonder is whether or not these games share the same engine, because if so we could reduce them down to
illusion_soft_(medium), since one has to wonder just how many folks search for individual images of these games, or rather, images of their favorite characters in them.
If you are talking here on dan, then not a lot, since getting images of either system through is so rare that searching for them is worthless.
If you are talking about searching for them in general, then god yes. Koikatsu is incredibly popular on Pixiv, and gets plenty of people either making artwork with it or just creating characters for others to make. Honey select is considered the "Better" (Read as: More realistic) variant, for people who want to make things that resemble humans more than anime characters. Both get some pretty extensive uploads alongside people making good money off of them.
I'm more familiar with the former (easier to mod, Honey requires a lot more investment to get up and running), but overall I'd say tossing all of them into an Illusion meta is not going to go pleasantly, since people have specific tastes with how realistic they want their characters. Easier to just make specific Meta's so that way we don't have to come back here later to fix the damage.