i recently reached the 75 pets at level 25 achievement (and got the no-longer exciting reward of a level 1 rare critter). since there is currently no higher achievement for leveling, i no longer have any means of tracking how many pets i've leveled (other than manually counting them). which means leveling joins unique pets and captured rares in the ranks of "things the game used to track for you but don't no more." so be it. it's not really that big a deal.
based on past experience, it seems almost certain that there will be new achievements at some point. what isn't certain is if there will be a "level 150 pets to 25", or if they'll simply introduce a new level cap and have all the achievements point to that, eg, "level 10 pets to 30" or whatever. given that the current achievement counts dings and not actual pets (allowing you to double dip on non-rare pets by stoning them and re-leveling) i expect that any pets i level to 25 now won't be counted towards a hypothetical new achievement. mildly annoying if my completed work isn't counted, but it could be severely sucky if i level so many now that the only way to hit the new achievement would be to release existing 25s and catch new pets. hrmmmm.....
probably best if i don't think about it.