So with Ria being for meleers and all, have you ever thought of ranger/magic paths? For the ranged path, most of the "evils" have their own gun/bow already, and while the "good" biomes only have repeaters, guns could easily be added. For the magic path, each biome has its own tome spell, so only the combinations would be necessary. Of course this would involve changing the Broken Hero's Sword into a more generic version (or one for each path, but that would soon turn into a battle with RNGesus) if the other paths would even use true versions.
I can't say the magic path would need true versions, mostly because I don't know what a True Golden Shower or True Miasmic Haze would look like, but I would imagine their combinations would be quite interesting. Imagine a Cursed Storm/Crystal Fire, or a Golden Beam/Arc Shower, or a Misasmic Glare/Aember Haze spell! I don't know if they should all combine in the end like Ria, but I'll leave that up to you.
Again with ranger, I don't know what a True End Render or True Undertaker would do (also, the Corruption really needs a themed gun rather than a musket). I guess I don't really know what the combinations would do either, since the "good" biomes don't have their own guns, but I'm sure they'd be very kewl.
Anyways, I love all your concepts and hope they find their way into 1.3 somehow!