The problem with the opening achievements is that they only work if both players do the moves in the right order, so no transpositions are allowed.
You can be a hardcore London player and never get the London, because it requires your opponent to play the right moves as well, and if they do it in a different order, you don't get the achievement.
As a relatively new chess player (and a true collecter of all things), I love the achievement system. Especially the section that allows me to collect the Book openings I have played. In my case, it incentivises me to study more openings, try new things and consequently become a better player.
Because of that, it would be really nice if at some point the library of openings that can be collected was extended, perhaps with more solid openings, maybe a "B-tier" (questionable) openings list, or with a Gambit library. It would add another layer of engagement and it seems like good fun to try a lot of strange openings I've never heard of.
Let me know what you think of the idea!