This doesn't seem like the right kind of site for this, many people just use this to make skins or upload/update a project and then leave. The online indicators already exist and you can tell how active someone is by plenty other metrics already, this would just be numbers for the sake of numbers, and imo a creepy one to collect at that.
Minecraft servers also tend to have login streaks because you'll get their digital currency that you would otherwise buy with money, or go to a page with an ad that nets them some money too. PMC does not have the first thing or a use for that and I hope it never does. Tying it to XP would also totally defeat the point of that system being to incentivise interaction and sharing of creative stuff and not simply passive usage.
Login Streak Like On MC Servers!