Im not aware there would be any restriction in 5e about multiclassing ...
As far as i know, you can quite easily be all classes ... nobody do that, bcs it sucks, but it was never forbidden to my knowledge.
Aswell as stat rolling to my knowledge never got any official statement suggesting we cant have it.
On the contrary, some sources suggests it was confirmed in the past ... so by usual rule of "what i say apply until i say it dont apply anymore" it should be basicaly confirmed at this point.
