Imagine a whole new minigame-ish gameplay aspect for the next, powerleveing-themed (level range 70 to 9001), expansion - hearthstone tuning.
Using your hearthstone is not a yes/no thing but you have to manage cooldowns. If you use it too often, it might overheat, incurring extra cooldown penalty (duh) or even taking damage and then having a longer cast time, which it will generally have while hot.
With some expensive effort engineers are able to repair damaged heartstones … to a degree. They can also make hearthstone coolers with coolant refills as consumables. A fully tuned hearthstone could be like a near-instant combat escape.
There would also be other tuning options, modding, like multiple destinations saved in memory.
So there would be such and maybe other special means to help it cool down, so that it is ready sooner. And also, if you overdo it and don’t cool it enough, it will burn a hole in your pocket and then you have to post a lost-and-found player quest on the player quest board where other players search the world for your lost hearthstone. (With various classes having their own special locator abilities. Hunters have “track lost items”, mages “scry recoverables”, warlocks “summon loot” and rogues … well, “pickpocket” of course, kind of a dual-purpose ability in this context, although only recommended if your gloves have fire resistance.)