I think CTE is going to go way up, due to the influence of these promotions. Way up.
A few reasons why:
1. Defensive excellence is being downgraded in terms of score, so fighters literally will not learn it.
2. There is going to be a lot more head hunting, which isn't the traditional form of fighting.
3. Thais learn to fight at a younger age. To some degree this is mitigated by the strong emphasis on control and defense oriented scoring, the lack of head hunting. But put 1 and 2 together, and bring it to younger fighters, its going to be epidemic.
It's really hard to speak now about "Muay Thai" because even within 5 years the sport has significantly changed, and maybe more than once. Fighter skills have devolved, generally, over the past 15-20 years, but now with Entertainment Muay Thai driving the sport you are seeing very different fighting skill sets (less fluent). And, one imagines its just going to get worse, unless there is a backlash in Thailand.
Traditionally though, the knockout wasn't chased in the sport, and the defensive awareness and boxing acumen of most fighters kept everyone pretty safe. We've met and known many, many high fight veterans and legends of the sport and almost none of them exhibit obvious signs of CTE. And most of those that do, that I've thought to take note of, have also fought in other combat sports after their career.