I publish an extension, Textcelerator (https://textcelerator.com) off-store. This is the first I'm hearing about this, and it would completely the sign-up flow for my extension. (My extension is in the Chrome store, but my landing page doesn't link there.)
Fortunately, it seems this only affects the head versions for now, not the version regular users get on a new install (I just tried it) or an autoupdate, so I have some time to switch links around and make it work. However, I really think there needs to be some sort of deprecation before this is rolled out, probably in the form of a warning on download if Developer mode is enabled, backported to versions 19 and 20.
Its mentioned further down in the comments, but if youre on the Chrome Store already, you can use Inline Installation. This allows you to use roughly the same flow you use now.
Fortunately, it seems this only affects the head versions for now, not the version regular users get on a new install (I just tried it) or an autoupdate, so I have some time to switch links around and make it work. However, I really think there needs to be some sort of deprecation before this is rolled out, probably in the form of a warning on download if Developer mode is enabled, backported to versions 19 and 20.