I'd love for plantsims to get a real deep makeover. I've only played TS3 and 4 so I can't say anything about the previous versions, but even TS3 plantsims seemed like a missed opportunity. There is a lot of untapped gameplay potential but they come off more quirky and cutesy. Have some of them take a darker path, ally themselves to ΜØŦĦ€Ř for instance. Have them be defenders of nature if you want them to be good guys.
And for the love of all that's holy, make them a permanent life state, and an option to create one from scratch in CAS if some people want to skip the transformation stages. I will say along with getting them by eating the forbidden fruit, bring back "Botanitis Minorous" from the science experiment gone wrong. We have a science career, add something where sims can volunteer for experimentation, just like in TS3, and have a random chance of becoming a plantsim.
I'm sure I will think of other things to add as soon as I hit post, but for now this is a start.
