Why hide it? It's quite useful for making something natural-looking. I mean yeah it'll still be easy to find in the search but so would anything else, I just don't know why it should be hidden?
Well, PLNT/VINE is really broken now, because it "infects" water like virus. It really needs to have a growth limit.
My idea:
When PLNT is created, it has a tmp of 2, and will grow once when it touches water or wood, then change its tmp to 0 and stop growing. If it absorbs some CO2/SMKE, it will have its tmp set back to 1, and can grow once when it touches water (but not wood).
This shouldn't break too many saves, since most people try to avoid the annoying PLNT+WATR->2PLNT reaction.
It would also allow there to be underwater plants that don't destroy everything
Vine shouldn't be hidden (yet) since the solids menu doesn't scroll, but if some new solids are added, then it can be removed to make more space.
you could continue using flag 8 for compatibility, since it is already used for SPNG and PHOT.
I like how VINE grows though, PLNT with a tmp of 1 doesn't do anything special. (I went "!set tmp plnt 1").