Doppelgängers & mimics the same?

D&D has a history of monsters whose shtick is to mimic other things: doppelgänger, mimic, etc. Quite logically, The Complete Guide to Doppelgängers posits that doppelgängers and mimics are different stages of the same species. This is such a fascinating idea that I have to borrow it. The two monsters have received plenty of variants in 3pp since that was published, which I would like to integrate. I don’t imagine that the two are linear stages: instead, I would write them as morphs that may be assumed due to environmental pressures. A mimic might mature into a doppelgänger or vice versa, then back again!

I will try to detail this further in future posts, with citations.