I think the LoC Vichy rules are much to complicated to be added later.
Given the complexity of WiF:FE in general, I'm not sure that LoC Vichy is too complicated for later addition. However, unless and until it becomes incorporated into RAW as an optional rule I don't think it's reasonable to expect it to come out in an official Matrix Games patch or upgrade (or sequel) to MWiF, and certainly not until Steve has had a well-earned (and hopefully long) break.
The involvement of US Entry chits, variable Vichy Geography, negotiations between the sides, purchases of units, territory demands, political consessions, and Vichy loyalty variations, would result in many modifications in a lot of areas of the game program.
The way entry chits are handled in MWiF makes that less of a problem than in cardboard WiF. The variable Vichy borders could be handled by CSVs. The negotiations are tough, I agree completely there. Their easiest configuration would be hotseat or live LAN/Internet multiplayer, and that would be hard enough. Harder still is PBEM.