@daughter@husk.site @sean both gmail and outlook.com can be problematic, not really in terms of migration but dealing with them as recipients. So much bullshit done in the name of "anti spam". However it isn't an insurmountable problem, as if it gets worse they'll risk regulatory smackdown (at least outside the US).
I've self hosted my email for longer than gmail has existed. So far, if you make sure you've got valid SPF, DKIM and DMARC you're fine. Maybe make sure PTR record matches MX just in case.
@sean @daughter@husk.site my situation is not typical since I've never done anything important with my gmail account--mine is a throwaway account I created just because of the hard sell Google gives you when you set up an android phone. If I had lots of data to migrate or lots of contacts who knew only a gmail.com address, or was just learning how email hosting works now, it would seem pretty intimidating.
Re-federating email is very important but will be very difficult.