After updating, the game will load like normal until the white screen with the Minecraft logo and the loading bar, and just stay there:

It'll just stay there, doing the usual animation it does until the game is manually closed. No crashing, no background music, just endless loading. I did leave it running for 30 minutes, which did nothing, then I left it running for 11 hours, still nothing. I was able to get the game working on 1.9.0, so it has to be something related to the beta itself