Does 'player discipline' not imply some kind of punitive system? If not I don't really understand your point.
If Powerplay 1.0 had been a runaway success and chock full of engaged players, they would not be doing a 2.0. So yes, that is a risk worth taking.
The way I see it, there would be certain aspects of the proposed mechanic that would simply be unavailable in solo/private mode. For PvP'ers to have an actual game, a tiny part of Elite would have to be exclusive to open play... this is not an unreasonable position, many online games do this. For example, they could lock Powerplay expansion related actions to open - considering its an aggressive action against other players interests, this would be appropriate.
Some aspects of the mechanic (PP2 or whatever) could be left available to solo or private groups. Defensive actions such as fortification would make sense to remain cross mode.
The point is to give everyone a role... the problem is when every action is available to the solo player, it makes PvP and open play actions superfluous by default. Then the PvP'ers just return to ganking whoever is about. The downward spiral resumes.