That's why it's a messy idea and very unlikely to happen. If the federation members are not unanimous, it just creates a whole bunch of internal problems. Likely UEFA is not going to be unanimous because at the very least Russia has interests to support Blatter to the end.
CONMEBOL is a different subject because not only is it smaller and therefore easier to consolidate, but they might very well get hit by sanctions stemming from either all their corrupted officials getting arrested, or by Blatter punishing them for lack of support, or by Blatter taking away a spot to give it to Oceania like he just hinted in his victory speech.
But all of this is extremely far-fetched.