Why isn't there a PBE game mode?

Wouldn't testing be much more efficient if there was a game mode on the live servers that gets all the current PBE updates? Players also would only have champions that they actually own, and maybe just get access to all unreleased skins on the game mode. This helps to make the champions players choose be based on what they actually play rather than a bunch that they don't actually have access to/care about.

Seriously why isn't this a thing. The balance team has said countless times that the data they gain from play tests and the PBE server is nothing compared to the data they gain from releasing to live. Maybe that's because you have such a small player base on the PBE, many of which probably don't care about testing things.