In my opinion, all melee weapons should be stitched. (Besides those certain No Auction ones like the smashy, slashy, or stabby versions of the Staff of Power).

It's pretty flexible to stitch Smashy/Slashy weapons and Slashy/Smashy weapons. Smashy/Slashy weapons are large two-handed weapons and Slashy/Smashy weapons are swords and shields. Those weapon types don't even have the same animations.

Stabby/Smashy and Slashy/Smashy weapons have the same animations
Staffy/Smashy and Smashy weapons have the same animations
Stabby/Staffy, Slashy/Staffy and Slashy/Stabby weapons have the same animations

(Some have different animations for Mighty/Brutal/Vicious Charge)

None of those can be stitched, but they are all the same.

So at LEAST the weapon types with the same animations should be stitchable, and I would be very thankful if ALL the melee weapons could be stitched together!