This probably ties in very closely with expanded leaderboards on the backend, but I'd like to have support for players receiving certain rewards upon hitting certain milestones.
Between this and expanded leaderboards, it's worth tracking just about everything we can think of on a per-account basis. More data is good data. This also gives us the ability to aggregate that data and draw from it for future balance work.
Off-the-top-of-my-head incomplete list of things to track
W/L vs every target individually
Count of times playing with each mark
Count of times playing with various types of decks (mono, duo, trio, quad, bow)
Count of times playing with each element (more than 50% of a deck is that element)
Number of new decks built
W/L for each coliseum event
Count of times coliseum is fully completed
Count of times receiving any given end-of-match bonus
Count of cards traded, by rarity
Count of packs bought, by rarity and element
Count of auction house uses
Net profit from auction house
achievement rewards
In most cases achievement rewards will be cosmetic rewards, but we can probably throw some card/gold rewards on early on too, so support for arbitrary prizes would be handy. Will put together specific list of rewards once supporting features are ready.
Relatedly, a long time ago, we'd talked about making every bound card unbound when a specific account hit 1k wins. Still pretty much up for that, including shiny nymphs at this point. If people want to farm shiny nymphs with alts by grinding over a thousand games on alts, that's a huge enough expenditure of effort that I don't feel the need to bend over backwards to stop it.
display
This is more for UI but is tiny so I'll just mention it on my todo list and not give it its own thread. Add a new "account info" screen (or multiple screens given how much data I want) that shows all the account data. That window can include the achievement list too.