FWIW, I've pushed a reworking of the config-file-finding, with the following shed-paint color choices:
* File is named <executable-name>.virtual.conf (I kept the .virtual, despite it being longer and not strictly necessary, because I think it more clearly expresses the function of the file. The existence or absence of this file changes Python's behavior significantly, so I think its name should be quite explicit.)
* <executable-name> has the extension stripped on Windows, but not otherwise.
* Config file can be located adjacent to the binary or one level up. The default sys.prefix is always the directory in which the configuration file is found, but can be overridden with a new "prefix" setting in the config file (which can be a path relative to the config file's location).
* I eliminated any form of generically-named config file, as I think the extra possible names (and thus possible sources of confusion) is not really worth the benefit. The only use case I can think of is if you have multiple python binaries or symlinks next to each other and want them all to use the same virtual config - and I can't really think why you'd want multiple binaries in that case.
Substantive comments on these choices is fine, especially in the form of presenting real use-cases I'm not currently allowing for.
Testing that reveals a flaw in the basic operation of this style of virtual environment is much more useful. The bikeshed colors are easy to change, but I want to be really sure this thing actually does what it's supposed to reliably before I go presenting a PEP for it.