Can no longer email myself a .epub file and open in iBooks? (used to be able to)
This feature hasn't been changed in iOS, so either the mail transport or client isn't faithfully preserving the file or you iOS device has issues and needs to go through troubleshooting.

If you have a second device, you could test setting up your mail account and see if it's a temporary (or permanent) mail issue.

Otherwise, you'll need to work on narrowing down why your device isn't working as expected.