I have a lvl110 boost awaiting use, and I guess the shadowlands one which tbh I dont think I will pre-purchase and instead will wait to see if the exp is worth playing.
Anyway my question is, since lvl cap will be completely redesigned ¿What happens with theese unused boosts? I’m guessing they don’t just expire? are they revamping them as well when shadowlands releases? thanks fam. I guess I really want to save those for the new races when the rep req is removed.
There has been no official news on this yet, but the one thing that we do know is that current lvl 120 will translate directly to lvl 50 in 9.0. So any current 120 boosts that people have saved will become lvl 50 boosts in SL (unless they decide otherwise).
As for 110 boosts, this is where we’ll just have to wait and see. My best guess can only come from the numbers we currently have.
Lvl 120 = lvl 50. This we know.
Also, 10 levels out of 120 is 8.3% of the total levels.
8.3% of 50 levels is (rounded), 4 levels.
So the best I could give you at this point is that a 110 boost would be equal to lvl 46 once shadowlands comes, but I wouldn’t be surprised if they rounded it to an “even” 45 just to make the number nicer.
Or they could make it something completely arbitrary and just proclaim that “110 boosts are now lvl 40 boosts because we say so.” Or [insert lvl here]. Really just one of those things we’ll have to wait and see. 
When an expansion gets rolled into the base game, purchased character boosts don’t expire but the free version of the expansion that gets rolled in will no longer give them as the rolled in version wasn’t a purchase.
Character boosts are some times up graded. When BfA came out, I used character boosts I had left over from WoD. They were originally level 90 boosts that got upgraded to level 100 boosts. The boost that came with BfA was 110.
Honestly this makes the most sense. Especially with the squish what would the difference really be between a 45 and 50 boost at that point anyway, except to cause confusion. I’ll go ahead and throw in my wager that 110 boosts will be “upgraded” to lvl 50 boosts while we wait for the blue text to enlighten us this summer or fall. 
Just a heads up… this is a player to player sub forum. Blues seldom check posts here unless someone has been reported for something.
Your best bet might be to keep an eye on the blog post that reported the level scaling changes.
I didn’t mean a response to this thread. Blue text meant as in updates leading up to shadowlands. 