In the TOS, Romulans were originally intended to be the big arch-nemesis of the Federation but giving them the ears was too expensive so they created a lower-budget race. They were never happy with that, and after TMP, Roddenberry's explanation for the changes at the time was that it was merely a retcon... "Just pretend they always had the ridges in TOS". In light of Worf going back in time to the TOS in DS9, they had to mention the issue but didn't canonize an actual in-universe solution until the end of Enterprise, thus also explaining why the Klingons had the ridges earlier in the series until the end.
They intentionally didn't use Klingons as the villains in the new Trek, and the deleted scene had them wear helmets so as to not reveal what was underneath. Even if they were ridgeless Klingons, it made sense for them to have helmets with the ridges to help them accept their loss of racial pride and identity that many Klingons undoubtedly felt because of the Augment Virus making them more human-like.
They should have the ridges in the new Trek.
They could just explain the Klingons learned a lot from having the Nerada for 25 years and one of the things they learned from the medical databanks was a way to end the Augment Virus plague before it had completely run its course.
My point is, the franchise waited until the end of Enterprise because it is really lame for Klingons to not have the ridges, thus the ridgeless Klingons only existed from 2154 to about 2270. Now they have the budget for them, so it is better to just make up an explaination and put the ridges back in the new timeline...
...If there needs to be Klingons at all. They could also just create original stories with more original characters and not show the Klingons in the new Star Trek. Then it's a non-issue.