How I would implement leaguestones into the core game

Normal stones drop like quest items on defeating certain maps under certain conditions, just like shaper orbs. You could even have a questline in there where you get the first one for free and have to beat map X with that stone to drop the next one. Normal stones have unlimited use and can be put in map device. Normal stones are balanced like its just like playing the league, if its Breach you MAY see breaches in your map. Zana will provide a new "craftingbench" that has x number of slots to store quest items only. This will provide storage for shapers orbs as well which nowdays is kinda awkwardly stored in crafting benches. Done, everybody get to play their favourite leagues forever (or keep it vanilla if they so choose) with a nice risk vs reward balance (see RIP videos from legacy, mostly beyond/breach). If Cardiro or whatever is too OP just nerf the spawnrate.

Magic leaguestones may drop rarely and have limited uses. Zana may sell magic stones from time to time.

Not going to happen. Before Legacy the only access to old leagues was by spending chaos on Zana's device. Better to just have leaguestones sold by Zana for chaos. Maintain the same system of using leaguestones and the Zana provides access to leagues for chaos functionality returns.