Deploying your software to these different stores probably doesn't involve as much friction as you think it does, and if there is a proliferation of stores one could imagine services springing up in the space to facilitate multi-store deployments and to make the process easier on developers. I mean, if it really is such a worry to you then someone will make a product to help with it because it is a business opportunity. TestFlight, after all, was invented because beta-testing Apple's apps used to be (more) awful.