I do not think Pirate Factions involving themselves in the current FW system makes them more interesting. If anything, it can turn off the consumer base because every other NPC faction is now involved in the endless grind that composes FW existence.
Well pretty much everything in eve is endless because it has to be, this doesn't automatically mean its not interesting. It could be, but it doesn't have to be.
What LP would the Pirate supporters get? Empire LP or Pirate LP? Pirate LP would have to be fundamentally re-balanced because their LP store is entirely different than Empire ones. To introduce a new source of LP without changing it would rock the markets and game balance.
Obviously they'd get stuff from the pirate LP store, getting stuff from the empire LP store would be odd. As for re-balancing, CCP could apply a LP payout formula that works with the current LP store prices of pirate lp store items.
Of course, the pirate LP store only contains 19 actual items (bpcs, ships, pirate implants), the rest are either pirate ammo, which is inferior to empire ammo and barely used anyway and hardwirings which are identical to the empire stores so their costs could simply be copy pasted. So overall not that much work, its less work then developing a new feature and would have to be done anyway if CCP were to add a new feature for pirate factions.
Existing Pirate content (what little there is) is hard to reach, yes. This is a symptom of a greater problem in which CCP doesn't respect the Pirate life style. We would have to split our discussion off to address this in more detail.
You tie in the Pirates to the Empire militia system ... again, rebalancing of their LP store if that is your 'reward' for fighting for them. Development time would be spent on that rebalance, which has greater implications that simply eat time being verified for balance. Why upset the environment for a 'patch in' feature when you could set a block of time for a proper feature? If your reward is access to the Empire militia stores, this issue is invalid.
Because there will never a block of time for a valid feature. CCP has to assign their development time to parts of the game their customers use and/or can use. If i look at curse there's maybe ~100 ish people running missions for pirate factions. This is in a region with lots of stations and lots of agents, the numbers for other smaller regions like fountain or venal are most likely lower due to it being easier to camp the hand full of useful agents in those regions.
Lets go nuts and say there's 2500 players doing pirate faction missions in eve, eve has like 400.000 subscribers these days, that means 0.625% of the eve player is doing this. CCP is not going to spend 6 months and an expansion to create new system which only a tiny fraction of the player base has access to.
Of course they could add a sec-for-tags like mechanics to open up this new feature for the rest of the player base but this is a fairly sizeable feature on its own, requiring even more development time while theres 20 to 40 features that large chunks of the player base use that need iteration/fixing.
So, wait another 8 years and hope at some point CCP finds time to work on an interesting feature or shoehorn pirate factions into existing features so theres actually some new content on that side of eve and hope that eventually enough players use it that their share of the player base becomes big enough to worth investing development time into?
Your reasoning for the Serpentis can work, although the specifics I don't agree with. It can be good business for them to enlist Capsuleers to destabilize an area. That would be the militia system for them; now what's the militia system for the other four?
'Sansha's invasion of highsec is a giant failure' ... is a rather generous means of looking at it. I will digress from the storyline reasonings, as we will most likely get caught up in too many divergent points.
From a storyline point of view Sansha made big claims in that expansion trailer and the end result is that every wormhole he opens to high sec results in the sansha fleet getting curb-stomped for a week and then retreating home to try again somewhere else. That strikes me as a failed/failing invasion and given the resources Sansha loses with every one i dont think its wrong to call it a giant one.
Of course in gameplay land incursions are pre-rigged for capsuleers to win (and even if they dont win theres no penalty.) Incursions would have been far more interesting if they started out in a single constellation and if players didn't complete that incursion before a certain time limit it would spread to adjacent constellations.
The constellation they now lost would have permanent penalties (nothing too big to prevent the high sec dwellers from quitting eve, think a 10% penalty on ship resistances, 5% higher market taxes, 10% lower bounties, etc) though the actual incursion would end until players push back the new incursions and then re-conquer the lost constellation.
Rather then being a constellation sized farm fest incursions would actually look like they're trying to achieve something with borders being pushed back and forth; if players spend too much time farming and not enough time actually closing incursions the rate at which it spreads increases exponentially with every new system it conquers.
The catch behind the system is that the timers adjust based on how quickly players can close incursions so that closing the original incursion is almost impossible but also prevents all of empire space from being run over. Now you've got the endless gameplay feature that the game needs but also makes it more interesting then just being a plot of farm land that grows isk.
Of course CCP is hesitant to shake up high sec since a large portion of the player base lives there and expects to be able to live in peace.
Anyhow, this was not really the topic of discussion to sum up my point: Ideally id like to see CCP add a FW like system for pirate factions based either on pirate factions in general or tailored towards the individual pirate factions.
For this to happen two things need to happen:
1: The percentage of the player base using pirate faction content (currently this is only missions) needs to increase by a lot for it to become worth spending development time on this.
2: In order for 1 to happen there needs to be more people can do with/for pirate factions then run missions.
So; adding pirate factions into FW in a limited capacity (just shooting, no system capturing) would be an easy way to expand gameplay on the pirate faction side of eve. It would require relatively little development time and open up this side of eve to a large portion of the players.
Once people are actually using it CCP will be able to justify development time into reworking the pirate faction FW into something more unique or replacing it with a different system.
Which leaves a choice: Make due with a feature thats not perfect and hope it will pave the way for iteration or wait another 8 years for something to happen?