Take a second look at the possibilities of XML modding, they seem to go quite deep.
Looking at what Heavenfall has shown possible with special resources, you may well be able to create colored mana by creating special temples per kind of shard. It's less clear whether you could create spells that consume colored mana (but WOM had spells that needed you to have a certain kind of number of shards), and IMO unlikely that you could get a "1 fire + 3 any" mana mechanism like in Magic The Gathering.
While this doesn't look exactly like what you seem to want, it may let you get closer than you think currently.