Please read my post. You obviously didn't. I mentioned your exact point. I'm referring to basically a quarterly reset where upon a new expansion no one has the reward/buff. But once you get all of the new grimoire for the new expansion (just the new points NOT all of the points since the games launch - NOT max grimoire), then you would get the reward/buff until the end of the expansion - it would reset again at the start of every expansion. This is only a bonus for continuing to play an expansion till the end.

You didnt actually say in the op that completing previously available grimoire wasnt required. In any case i dont think this is a good idea (and apparently 70% of the people who replied to your poll dont either). It would incentivize players to overgrind way too much. A cosmetic reward for maxing grimoire score would be a much better idea.