Not anymore. After public outcry, Google established 2 alternatives:
Through developer mode, you will be able to “forego security” (according to Google) and do a lengthy and obnoxious procedure to unlock your phone for installing any app.
They’re defining a way for official (sanctioned by Google) 3rd party app stores to work, and you will be able to install apps verified by them, instead of Google.
Not anymore. After public outcry, Google established 2 alternatives: