Maybe it would be worth asking Nival for the Heroes 5 engine? The idea is that it doesn't belong to Ubisoft, and it could be used to expand the game's capabilities without the source code. (I want normal graphics that would match the level of games from 2008-2010, not the thing they made in 2004. Apart from the smoothing, which doesn't work with transparent textures, and anisotropic filtering, they didn't add anything else, although that kind of graphics would have been relevant for 2004, but not for 2008, when the last expansion was released).
Various features were removed specifically so that the game could run and even work on video cards of the GT 5200 level (on chips from nVidia)... I don't remember what the top-end ones were at the time for ATi, but we didn't take them into account, as their share of the market among potential buyers did not exceed 1-5%.
