I’d be all in favor of myusername.*. Namespace packages are very easy nowadays. People would sure complain that it is more to type (or whatever) but import acme.library as lib is also very easy anyway. For reasons I can not pinpoint right now, in my mind acme-library feels inferior to acme.library. Probably because people would be more tempted to have a top level package library in project acme-library and imports would clash at some point later. It is of course also possible to have a top level package library in a acme.library project, but maybe less tempting.
Is it worth opening a new discussion or should it be added to the existing one “PyPI as a Project repository vs. Name registry (a.k.a. PyPI namesquatting, e.g. for Fedora packages)”?