Won't the lockup expiry increase the float on these already-included companies, forcing mechanical buying by all the very large pool pool of folks holding these index funds? Thus creating forced buyers to maintain said share price?

They will have a big impact if they can maintain share price AND the float increases due to the lockout period expiring (ie. pre-IPO owners selling off shares).

I'd like to know how the CRSP/Morningstar folks feel about the interesting lock-up period rules that Elon has inserted into the SpaceX IPO and how that jives with their analysis.