devtrackers.gg
As someone who doesn't play ranked very often, I've always seen champion mastery (and eternals) as a way to showcase skill and good usage of a champion in League. It's always been my personal favorite system that the game offers because of the fact that it's the only real reward I get from playing champions I enjoy, and it rewards me even more for being good at them.
I recently saw a twitter post from one of the rioters saying "there's no point in releasing a feature on time that people aren't excited for" (direct quote) so I'm hoping that others will boost this post and show Riot that we do actually care and are excited for the changes because I know I'm most likely not the only one who enjoys that aspect of the game.
I obviously don't know how programming the game works, or what changes they're making to the system and what could be causing further delays, but if one of the main reasons they're not working on it is because they don't think we're excited for it as a community, let's show them that we appreciate the work they're doing and that we enjoy the little things too.
UPDATE: I just reread the original devblog and it seems like a few people are confused about how the changes are proposed, so here's some clarification.
Mastery Rank is not resetting each ranked split. The reward system associated with ranked splits seems to be separate from overall mastery rank itself.
Mastery levels will not be lost upon release of the new system (I thought this was obvious already but I digress) they're just adding more levels.