-1
I think regular ashes giving prayer exp isn't really something I would support.
The urn idea has some potential, but it's a bit of an odd mechanic. Besides, prayer exp is already fairly easy to obtain. Would rather see a different use for the firemaking skill.
That said, I think the skill should only give minor, but useful bonuses/conveniences, think of agility.
Perhaps some kind of minigame with (skilling?) rewards? Or balloon transportation?
Nothing too game-changing or intrusive at least... And nothing that would upset or divide the community.
Edit: Something like Pyre Ships from barbarian training, with special bones dropped by high level (slayer?) monsters, or Shades of Mort'ton Funeral Pyres... Just an idea, and it could work on a much smaller scale.