i mean, double cylinder 310gs is possible, like the Kawasaki Versys 300. But Kawasaki had this engine already ready, based on their Ninja 300, while bmw does not. so I doubt that they would take this course of action. also, double cylinder in 300 range will increase the rpm significantly, and it is already so high. for instance, you have to rev the versys 300 really high to get to the minimal bottom end torque. i am personally fond of single cylinder bikes. they are not so strong, but they have their own unique character.
I have bikes with 4 cylinders, 3 cylinders, 2 cylinders, and 1 cylinder. each one gives you a different kind of joy in riding. still, my favorite is the old Royal Enfield (not the new one crap, made after 2010) with one cylinder. But it has pushrods (not overhead camshaft) and a very long crankshaft rod. it is like a like Harley but with one cylinder. they called bikes like that 'thumpers'.
as you love riding, you need to love you bike