I like this weapon, since is the "bastard version" od the rapier. Your "Epee Rapier", as well as Beltarfirt's "Striscia, are basically the same weapon, and I think they can be classified as variants of the "Elven Thinblade". I would be logic that characters proficient with the "Epee Rapier" are also proficient with Characters proficient with the Elven Thinblade.

I missed one thing: why the epee rapier, while counting as a rapier or as longsword for the purpose of feats, can be used as a longsword and not as a rapier? Being both piercing and slashing and missing the 1/2 strenght when used two handed, it should be considered closer to a rapier than a longsword...