It would be very nice if you could make the Gentoo package manager (aka portage) a virtual package. This would allow other developers to create portage enhancements or replacements. Reproducible: Always Steps to Reproduce: 1. 2. 3.
considering i know of no such drop in replacements i dont see the point if someone really wants to use something else they could inject the portage package ...
Or you could try PROVIDE="sys-apps/portage", not if it works. To make a patched version create a portage ebuild in your PORTDIR_OVERLAY, put all the patches you want in $FILESDIR and use epatch to apply them (that's the way I use for my gpp patched portage) or write a new ebuild from scratch. You can still emerge the normal portage by using the explicit version number.
Ummmmm... They shouldn't use the same name if it's not the official package. They don't use the same data, and they shouldn't have identical interfaces, so I don't see what the issue is.