Re: This is the right direction!
"We already have such a thing, indirectly. It's the tax on fuel. Drive a lighter car (all else being equal), it'll be more fuel efficient (as less dead mass to move) - cheaper motoring. Drive more sedately - same."
In the UK, that's not the case (yet!) in terms of EVs. Being zero emission at point of use (excluding tyre wear), they are taxed at the minimum level. Whether it's a 2T SUV or a microcar.
At some stage, that will have to change. I suspect though, that the change will be Pay Per Mile rather than a scale of VED charges based on weight/efficiency. It'll be difficult to charge based on electricity usage since many will charge at home. Smaller cars being able to charge overnight off the house ringmain/standard 13A socket and not via a special charger will be impossible to monitor for "fuel duty".
Successive governments of all colours have been kicking Pay Per Mile around for years now.