The thing with the bed is that the devs had to add new colored beds (they promised), but because there was no space for additional 15 blocks (and the removal of the limit was pushed into 1.13), so they had to make the bed a block entity. And because it's now a entity - its model is no longer customizable. This should be changed back in 1.13, after they remove the limit.
We aren't limiting progression any more than the current achievements - we'll recommend you do x before y, but if you do y before x then that's entirely your thing!
Mods or maps or anyone making their own custom advancements can change that, of course. This is the decision we made for vanillas own advancements.
Rollback Post to RevisionRollBack
GENERATION 37: The first time you see this, copy it into your signature
on any forum and add 1 to the generation. This is a Social experiment.