It's an interesting thread, and reveals some of the hopes, fears and concerns involved around OOPP.
What if for a moment we accept that FDev will "never do open only anything" (plausible). And that really the game is a multiplayer capable game, rather than true MMO; even when everyone is in open it can be frustrating (<ahem> instancing). An alternative has been discussed repeatedly, of harder NPCs replacing the threat of players in closed modes to create a more level playing field across modes. To me, this almost feels the wrong way around, NPCs are commonplace, players are rare, partly due to instancing.
So here's another idea - players replace NPCs, when players are present. This requires that there exist some (opt-in*) NPCs that present an obstruction equivalent to the average player, in terms of being able to successfully interdict, to hold a player in instance, and to require a player in an engineered ship to actively avoid destruction, even at times in no-fire zones. These comprise the real endgame(-ish) PP opposition, with players standing in where available. Harder, not more, NPCs - otherwise they become merit farms, or just bothersome. So:
1. Default threat (and presence at all) of certain new, specialist PP NPCs is progressively increased to average-player-level hazard with increasing PP rating, when a player reaches a rating above 3, *so it remains opt-in, only affecting hardcore merit movers, not module shoppers
2. For every hostile pledged player currently instanced with, the NPC threat is diminished proportionately ("player replaces NPCs"), regardless of mode
3. Default NPC threat level for a player of a given rating is decided as a function of the number of instanceable enemy pledged CMDRs in the same system and cruise level/POI as the player (could be encountered by the player in open or in the same PG; do not have the player blocked in-game or via router) as well as rating, combat rank and loadout of those CMDRs. This could be capped (since player instancing is limited).
4. NPC threats combine in some way if multiple allied CMDRs are instanced together in system, regardless of mode (equivalent to players calling for aid). Again, capped.
It's not all new stuff, and I'm not addressing any technical challenges, and some exploit checks and balances needed, but here are some standout features:
Everything remains optional and opt-in, every mechanic here is pan-modal, and only addresses feature balance. With this, the competitive incentive to avoid open is mitigated, while full merit earning capability is available in all modes.
Module shoppers, casual players and players flying in systems empty of other players are not impacted in any way.
Block function is unaffected, but removes a player's ability to increase NPC threats encountered by players they have blocked. Just as they would not be able to directly attack a player they had blocked.
This requires no other change to the current PP system, and most people won't notice it.
As a confirmed career ganker (= I fly in open), my disappointment is immeasurable and my day is ruined by the fact that I came up with an idea that isn't simply open-only.
This focuses NPC resistance on locations that matter (as decided by players), and has a chance of making the single player experience more varied, interesting and meaningful.