I don't like it and I don't really understand how it's gonna play out wholly.
I get the film and their origin is going to be set in a 'separate' universe and given we are embraced within the multi-verse now (thanks to Kang etc.) the integration shall come later, but for me, it's the 'what comes later' bit, which will 'spoil' the casting as such.
Will Doom exist, in other universes as well, so we have a separate casting for 'another' Doom elsewhere or is RDJ going to be the definitive one, with all the history tied to Reed etc.
It also, for me, rides all over the entire previous phase dynamic with Tony and all his sacrifice meant at the end of Endgame, equally rumours of Steve Rogers' return will do the same if he plays the character, it's been suggested he will.