Shadowlands Timewalking & Future Level Cap

As of right now, this is a completely hypothetical scenario, so I understand if nobody can answer this. I’m curious about the future of timewalking when Dragonflight releases. I already know that they will raise the level cap to 60 for timewalking with the future expansion, but I’m not sure if buying an Experience Eliminated buff will do anything to help. I subscribed to WoW earlier this year, but I did not buy the SL expansion because I knew DF would most likely release later this year. Since I started playing WoW, I have created three characters. This is my first character, and I have two Horde characters. I’m planning on making my second Alliance character a Dracthyr. My intention is to wait until DF releases and then do SL as a timewalking campaign, so I wouldn’t essentially be paying for two expansions at the same time. My problem is, since this is my first character, I have already done a lot and progressed quite a bit past the level I currently am. I was wondering, if I purchased the Experience Eliminated buff at Level 50 (without SL Expansion), will that even matter once DF rolls around? In other words, will I stay Level 50, or will I automatically be leveled to 60 despite having an Experience Eliminated buff?
I’m the type of person who likes to make my characters unique in some sort of way to make them stand out from each other. I generally don’t like having to repeat the same questline as a different character, so I try to put each of my characters in different scenarios. The problem is, I don’t want to have to create new characters only to have to level them up and therefore make my original characters obsolete.

(Second Character)

(Third Character)