How likely could GMail follow the same path ?
Specifically, Gmail had 1GB quota at launch. These days you have 15GB combined across Drive, Gmail and Photos for free, and paid plans if you need more space.
https://news-cdn.softpedia.com/images/news2/Undo-Gmail-2.png
I've been running that setup for a few years now and it has been flawless. Spam is almost entirely gone, with a catch-all address I can simply sign up to websites with <website name>@mydomain, makes it easy to track down if one of them ends up doing shady things with your mail!
Should I go for firstname.lastname@hardtochooseamongwhatsleftdomain.com or mail@firstnamelastname.com ?
The mail@firstnamelastname.com approach seems like a clean way to do it as well.