1st generation processor=sense 1.0(ex og evo, Droid incredible)
2nd Gen processors is sense 2.0 (ex evo shift, Droid Inc 2, desire HD others)
Dual core = sense 3.0 like the evo 3D and sensation ( tablets, also)
This is not too say the processors can't handle it, they obviously can, but that's HTCs excuse for not updating the sense version.
As for the evo being discontinued, it has reached it's end of life from sprint. This is not too say that updates will end though, although they will be less frequent and who knows there might never be another update...
Bottom line. Root your phone if you want something more.