Ember Online

You can heal by paying money at a temple, was always curious why you cant buy a mana top up. Be nice to implement it... what do y'all think?

HP pots will always remain useful because you can't run from an OAD/Event to heal or anything not to mention people don't often wan. I had thought of the exact same thing concerning MP too but refrained from posting it because it removes a pretty significant gold sink from the game making MP pots pretty useless. Your gold cost per mana regen would have to be significantly over cost of average necessary per mana costs in shops just to make it less desired so that people would still purchase mana pots from the store....which in the end throws everything out of balance for the most part.

Although I loved the idea at first when I was mulling it over I convinced myself out of it purely because I don't think taking gold sinks away is a good idea.

Aye thats one of the problems with this type of game (gold accumulation, most games actually have an eventual problem when it comes to wealth and items, economy in general...)
I am not quite convinced this would remove a major sink hole, but then I remember in some oads (etc) you usually needed speed, which meant glugging potions to get back there quick. Potions are used more on the spot to stay there though no? I never really took part in major oads, so cant comment fully.
Mana recharge should definetly cost more than a health recharge though.
As for sink holes, introduce a durabilty system Items need to be repaired, but lose permanent durability until their no longer any use...