I am also interested in getting Plone installed just in pip instead of buildout. I'm not looking to get rid of buildout per se, I just want to have the python environment regulated by pip and let buildout do other things. This may end up being a bigger ask than just going completely without buildout.
The reason for my interest is the python community as a whole has increasingly relied on venv/pyenv/pipenv/whatever as a given in any project. This historically caused problems with tools like Pycharm Good news for pycharm users where buildout support was de-prioritized because it represents such a small part of the python community. But there are other tools I've been looking at like ossaudit and safety that just flat out only work with a venv.
It looks like a lot of work has been done already since this issue was created. I was able to create a test environment with everything pip installed just fine (I don't know what the issue with z3c.autoinclude was or if that's still a concern). As others mentioned, mr.developer is still really nice for managing several dev src eggs and I'm comfortable using it to create several parts/executables.
As I test I took at pip installed Plone and a barebones buildout with just a plone.recipe.zope2instance egg. Every egg this needs gets added to the eggs/ section though, even if it's already in the venv. I don't really know the details of this, but I would guess this would be a problem with any recipe that uses zc.recipe.egg. Do we need to abandon these eggs and use solutions in other tools like Asko's plonecli changes?