I seriously doubt Beth has the skills required to develop a new system. Nor do they have the mentality to attempt anything really new.
Fallout 3 pretty much fails on any attempt at innovation and should be discarded. Any use of the term 'evolution' when referring to it should be purged.
It's a horrible shooter.
I mean horrendous.
You can't dodge, there is no cover in anything but the ascetic sense, and the use of health generally means you have to stand there and basically point a directional DOT and something that's doing the same thing to you.
Neither is a good RPG, for many reasons.
The combination of the two is pretty sorry as well.
Especially considering two games out with did combine the two genre's and did it quite well.
Deus Ex is ancient at this point but was a good combination of the two genre. It was primarily a shooter, but had RPG elements and you had skills that directly affected how well you did things. System Shock did much the same and was even older.
Mass Effect is a much more recent addition and was more RPG with Shooter elements, which is I think what Beth had in mind, but they have a very poor mind. ME had little use for twitch reflex and had target assist for the shooting aspects, but it allowed you to have tactical aspects and playing smart from a shooter aspect actually had benefits.
Beth wasn't exactly breaking new ground, just treading an already cut path... and they got lost along the way. They couldnt' decide whether to emphasize the shooter or RPG genre and birthed a pretty piss poor example of both.
Part of this could perhaps be laid at the feat of the engine, of course, but it was there decision to use it and if they didn't feel like trying anything new for a new franchise it is unlikely they'll try anything new for future projects. To them they still have a 'winner' of an engine that keeps making them money, so no real reason to change anything but the pixel resolution I imagine.