

At no point has Gmail ever said “we’re no longer allowing you to send/receive emails to/from Hotmail” or has Yahoo said “we’re maintained by a single volunteer who because of real life stuff can no longer continue so we’re discontinuing our email service.”
But this literally happens with instances all the time.
Interesting idea, but it would need to be heavily moderated against scams and such that have pervaded other online “handmade” shops.