I made a suggestion about something like this quite awhile back, but maybe it was before it's time.
We have several models of Norman and Kite shield, with bland generic textures on them. Why not take a few of them, and make oval shields, and maybe a coffin shape one. On ALL of the generic (non-heraldic) kite/norman/oval/coffin shields, just retexture them with solid colors. Red/Green/Blue/White/Black, etc.
This way, they can be used by people playing different cultures. The kite shield was a pretty universal design, used from the Iberian peninsula all the way to the Rus and Saladin's Saracens. Oval shields were pretty prevalent as well, so what would it hurt?