Given this some further thought:
I do not think long-time endgame players already enjoying your game will need much further incentive to buy the expansion other than the promise of new and fun content.
We'll buy it. We'll check it out. If it's cool, we'll continue to play it.
There is absolutely no need to artificially drive us away from the old the content we cherish.
I understand, however, that you also must appeal to new players and casuals.
So adding low-skill / low-commitment content is necessary.
A while ago, you marketed strike missions as an entryway to endgame content like fractals and raids.
With a mediocre raid team, you can just yolo the strike missions already in the game, without problems or much thought about their mechanics.
We are waiting for the strike mission CMs to actually pose some challenge.
We are praying for new raid wings (!) and fractals.
As a person with 'a life' and a job, I do not much enjoy repeating content or faming maps for currency (let alone gold). I play the game the way I like it, mostly because it is fun.
Of course, there should be some reward (also unique rewards!) to the different game modes.
I very much like the weekly rewards you added to fractals and raid CMs.
Now, it would be nice to have any real incentive to not only repeat the easy raid CMs, but also stuff like Dhuum CM - maybe on a monthly basis?
Try to maybe reintroduce some value to dungeons (with the legendary runes and sigils, those got even more obsolete).
Please give us a nice platter of options to select from each week, rather than pushing repeated strike missions or login rewards.