My 2 cents:
- the Ubuntu font has a lot more personality than Noto
- design wise it may down to preference, but nonetheless I think Ubuntu is not quite a top-tier font (but is better than Noto)
- the Ubuntu font really is thicker, which makes it a bit more legible
- Noto has crazy script support, beats Ubuntu in this category
- 11pt is great for laptops that need a scaling factor of 1.1 or 1.2, but represents a negative change for desktop machines
- the question of how well Plasma and the Ubuntu font fit together is worth asking, although we may just not be used to the two being paired
- it's also important to guarantee that upstream will not mess sth up, but anecdotally speaking, I don't think I've ever had a problem with this, and I always non-default fonts.