Regarding other missing child cases: in July 2020 Dutch police presented their case of a boy gone missing in The Netherlands in 1995 to German police after news broke of Christian Brueckner as suspect in the McCann case (and possibly other missing child cases).
Dutch police admitted that there wasn't any concrete link with their case and CB but that they felt obliged to reach out to German police anyway, and that in fact "it would be crazy not to do so".
So apparently this is just something that cold case squads do.
BIB - yes.
I was recently reading a couple of different articles about serial sex attackers, where a number of old cases were cleared / solved when an arrest is finally made.
I wouldn't be surprised if CB ends up being charged in 1 or 2 similar rape cases.