I don't like multiclassing if most of the disadvantages were removed. In my opinion each class should be independently monitored. So if I level Barbarian to 4 and put the next point into Rogue (cause later I want the two bonus actions of Thief for my Berserker), then I should get the lvl 4 stuff of Barbarian + the lvl 1 stuff of Rogue. But not the second action the Barbarian would get at lvl 5.

It's ok that they removed the ability prerequisites. That they want to make spells and maybe other stuff more easily available than "normal" led me to the conclusion: Probably don't use multiclassing in BG3. Similar to not using stealth or a lot of shoving in EA.

As that's much speculation, let's wait and see.