It would be very interesting.
My guess is that we'd use exactly the same method (our subjective observations) but they would be skewed very heavily to the last few matches that we can actually remember or else disproportionately weighted due to some outstanding feat that sticks in our memory.
The value of the MVP is that the ratings are given at the time of each game, so early season performance is still recognised.
Still, like any 3-2-1 system, it's pretty hard for a goal-kicking winger to make an impression. He'd pretty much have to score 3 tries or win the game with his goals.
Meh...
what does bearfax think??