Is there any scripts around that create a battle system like the Tales games? I.e: Your characters can run back and forth on a 2D Plane, V To open the Menu and select a party member and items M to attack and etc etc.

not to my knowledge (though I'm hardly the best person to ask), however I can easily imagine re-appropriate some of the ATB system codes and using them for just battle encounters.

I know people have made systems like this, but I can't say for sure if they extended the battle system or just made a completely new system.

I've had this thought in my head since I started using RMVX and I've always thought it was impossible

You guys underestimate rpg maker soooo much! Its definitely possible, my friend Aten made a system like this in rm2k3 (I helped solve some of the design issues as well), so its definitely possible in rmxp/vx.

That was amazing, honestly. Was this achieved with RM2k3?

EDIT: And that's me not reading more clearly. It was. I wonder if Aten could share his events.