It's about cost vs benefit. I'm sure it would be technically possible to have an auto coupler that can take traction power, the question is whether it's worth it or not. Every unit will need a pantograph anyway in order to operate singly. The benefit would be if there is an issue with a unit's panto, or with higher speed running with multiple pantographs up on shoddy OLE. ...
No, the technical issue wouldn't even make it operationally viable let alone have any cost benefit. The average 4-car EMU has between 1 & 1.5 MW of traction current requirement. An autocoupler with 25kV ac contacts would never be workable in a weather resistant configuration for reliability reasons, let alone getting safety clearance. So the next option would be to extend the bus between units. That impact of that would be:
The wiring and contacts would need a 2133A current capability.
The on-board transformer/rectifier of every unit would need to be doubled in size as would the bus line (or duplicated).
So all of that high-risk hardware on every unit would need to be balanced against the occasional need to recover a failed unit.
There is no problem with the very latest EMUs recovering their fellow units anyway, - because the class 700 Thameslink units are the only electric trains that can pass through the thameslink core, they have a capability to pull a failed unit out to clear the route. A 278 tonne 3.3kW 8-car 700/0 unit has sufficient power and tractive effort to recover a 410 tonne 12-car 700/1, even up the 1:27 ramps at each end of the core!