i have a little suggestion that might be worth considering.
in short (aka TL;DR ) : in addition to the mundane weapons/armor pieces, unlock some of the lesser champion-only weapons/armor pieces (like silver broadsword, toxic shortbow, warding kite shield etc.) to the shop. they could unlock with appropriate technology (i.e. add a champion-only shield to the shop at a tech that also unlocks a mundane shield for troops)
why i think that addition would be reasonable:
as it stands now, champions are in a good shape (IMO). they all serve a purpose and (can) change the gameplay significantly. melee/physical damage champs were finally brought in line with the improved itemization of the last patch. however, there's a small problem: if you don't luck out and actually find a decent bow/sword/armor/shield, they have a tendency to fall behind trained troops around the middle of the game (when troops start to become fairly powerful). that's a shame, since at that point, you invested quite some time into development of your assassin/warrior/defender and probably don't want him/her to be weaker than a group of generic swordsmen. it's luck based, for the most part. if you find that awesome shocking longbow or a druss blade or whatever, they still surpass the trained troops.
to reduce the element of luck, you could implement the above mentioned feature, which would also (in a sense) serve as a rudimentary "crafting system". you didn't find a good weapon and now your archer assassin is obsolete since basic archer troops do more damage? save up some cash (maybe also metal/mana/crystal/fame?!) and buy her a decent champion-only bow (that unlocked at the same tech as the mundane longbow, for example)
in a similar fashion, the magic tech tree could for example add adept/mage robes to the shop, and maybe also some of the champion jewelry (ring of ashes etc.)
i don't know how much effort it would be to implement that suggestion. if it's too late for the release, maybe you could add it as part of a "content patch" after release.
thanks for reading.