Am I the only one to suggest this?
I'm sure people will rant at me for making a thread about this, Because of things that don't make this such an easy thing to do, Or simply because I've made a bad suggestion in the past (Cough* Dual Wielding *Cough), But that doesn't change the fact that this is even possible.
Now, As for problems like not having items from other versions, They will still appear in your inventory, Just unusable. So as not to cause errors in the game, you will be switched to equipment you own that is from the version you switch to.
Putting aside whether or not this is even possible, why would a player want to go back to an older version?