The question is whether we get a one and done Doom (which is a bad use of Doctor Doom) or we get RDJ sticking around for years as Doom (which robs us of a Doom that has had a decades-long rivalry with Richards).
Ideally (?) we'd have a multiversal reboot at the end, and we have a new Doom who's "always" been part of the reborn MCU and who has "always" had a rivalry with Reed, who has "always" been part of the new timeline.
I'm not sure how audiences would feel about Crisis on Marvel Earths, though. We'll see what the plot actually looks like when we see it on the screen. (Lots of MCU movies have name-checked Marvel Comics storylines but not actually followed them that closely.)