The main problem I see with the M14 isn't the stock or it's lack of a pistol grip or forward rails, it's the lack of a flattop and rail over the receiver. A modern rifle should be built with an optics mounting rail that puts whatever sights are used at the same level so that you have a proper cheek weld whether you are using iron sights, a scope or a red dot, (I'd say NV too, but given the bulk of NV scopes, that's probably still unrealistic).
What would really be an effective modernization of the M14 would be to redesign the receiver with a Picatinny rail going across the top, (not some sidemount, but an integral rail), and then raise the comb of the stock and the sights about 1". I don't know how you'd disassemble it with the top of the receiver closed off, but that would also have to be part of the new design.
I really don't see any problems with the weapon besides that. The safety is different, but it's easy to operate and the traditional style stock works as well as a pistol grip stock. The iron sights on it are superb. It's reasonably accurate and pretty reliable to boot.