I've been thinking about adding a new game type with resource gathering and unit production; but that'll probably have to wait for an expansion, as creating that would be a huge endeavor.
It is also possible to summon Barriers or Charges that do elemental damage instead of explosion damage?
I'm pretty sure the answer to the question about Barriers is yes. You'd need to create a new character class with a movement of 0, create its attack, assign it that attack, then name that new character class as the thing being created in a new Create skill. The only thing is that right now, it wouldn't attack automatically, and would probably be susceptible to backstab. I'd have to double-check to make sure, though.
As for the charges: right now, Explode is the only attack that triggers upon character death--there is not currently any way to create an alternate version of it, although you can always go into the Attacks.xml and modify the Explode attack itself, including granting it a different element.