FUD.
The "architecture" change is the bootstrap repository, which has a new folder structure. I know, scary stuff! Folders!
The "architecture" has some enhancements to middleware and fleshing out events/commands to a "command bus". Basically, you get more sugar on top of the (mostly) same architecture.
Whoops caused a lot of headaches behind the scenes, and did stupid things like convert ALL http error responses to 500, even on a 404 error (which showed up in Whoops, as HTTP errors are converted to exceptions within Symfony's HTTP stack).
Blade tags have one new tag, and the old ones still works.
This point might be the subjective one - HTML library. HTML libraries create an enormous amount of support for people's edge cases and generally are better pushed out as a third-party add on to suit your needs. The upgrade guide explains how you can add them back in if you want. https://github.com/illuminate/html