One could make a case for why one-handed weapons are meant to be wielded in one hand and why they might perform worse when gripped by both hands of the wielder, possibly due to how they are balanced in terms of weight, or how long their handle/grip is. All that killjoy logic aside, would it be possible to have a general 'spell' (read: ability icon) that you can click to adjust your grip on your wielded weapon, allowing you to switch between grip modes. Using it would allow for the following grip styles:
One-handed weapon with two-handed grip - basically, you could wield a single one-handed weapon with an empty offhand slot, and with this grip style, the game and its mechanics would treat it as being a two-handed weapon for talents and RE mechanics and treat you as not having an empty offhand. Its damage/stats would stay the same, the only difference is that talents that only work with two-handed weapons would suddenly start working for it, while talents that only work with one-handed weapons would stop working for it. This should probably not break game balance, since one-handed weapons have lower stats compared to two-handed weapons, but there might be hidden gems among one-handed weapons in terms of effects that proc on hit, that you might want to have while playing a two-handed wield build.
And the same in reverse - two-handed weapon with an empty offhand (possible through Titan's grip and maybe hoplite?) treated as a one-handed weapon with an empty offhand, rather than being automatically dual-gripped by the wielder. This would allow you to benefit from one-handed weapon talents and REs on it (swashbuckler at least).
Both of these basically deprive you of an RE enchantment slot, since you are basically giving up your offhand slot (and its stat bonuses) to utilize these, so they would probably not be 'too good', but definitely flavorful to be able to do it.
I'd assume that from a technical standpoint, the animations should work, since you can already transmog this kind of stuff around. As for would these break anything in feral forms... not sure. One limitation that I would personally consider, if this gets implemented, is to bar daggers from two-handed grip, since there are limits to even rule of cool, and it would probably make it easier to implement, since you would not have to go through all those spells/talents that work different with a dagger and two-handed weapons.