Wow...
You obviously put a LOT of thought into this.

I actually love this, as it plays toward some of the same ideas I've stated in my own threads on the topic. I like the idea of the War Barge purchase being part of the invasion, and the shorter timer structure.

The only issue I could see is again running into the issue of time zones. Even if you still give an hour's warning of an attack, it doesn't do anything if the entire Corporation that owns it is asleep for the night, and if the game starts requiring players to recruit globally just to avoid getting steamrolled while they're in bed, we're going to be seeing a lot more angry people than we are now.

The 24-hour timer thing is a real killer, but I just don't see a way to avoid time-zone wars otherwise.

Interesting idea, I really like the amount of thought that goes into it, but I have questions/ concerns. Some are hard to articulate.

Are all these battles located on one district? If so, it would mean all that stuff will be going on on one map.

The shield relays are protecting the district, so shouldn't it be on the districts surrounding the one you're attacking? Or are the shield relays on the targeted district, but only shielding the outpost (or "city") and other important sites? I ask because its hard to get inside a district and fight on it if there is a huge shield around the entire thing preventing you from even getting in. I imagine the redline could be greatly expanded so a district could have lots of gameplay areas for the initial shield relay parts outside of the outpost part of the map.

EDIT 2: Seems like a lot of work just to take one district, I think such long campaigns should be reserved for districts with an Surface Command Center (something CCP mentioned, very important, 1 per planet). Perhaps the amount of points to conquer a regular district, and the amount of clones the attackers buy at a time to bring should be lower.

For Timezones, I like the Defense grid suggestion. I think its elegant and subtle and it works. You get a 8-10 hour window where you cannot be attacked. And if you are a really small corp you can fit 2 of them into each district slot and get 16-20 hours of invulnerability and only have to defend during your peak time, but you don't get any of the other perks.

OP has mysteriously vanished....

Kidnapped by CCP to fix PC maybe?

If the district could be configured just like a suit, it wouldn't be complicated at all, just sounds complicated on paper. It would be very intuitive in the UI, and when you attack the district, you could get a little popup map that makes it more intuitive for the attacker as well. You worked hard on your idea, keep it.

Thinking about it (Your idea, not mine), if we wanted to do battle types based on what you have placed.

Shield Relay battles could be like Skirmish, so you have multiple control points you have to hack. Except without the MCC (You don't want it to get blown up to easily in the first match of six, unless your warbarge comes with a like 6 pack of them, which would be cool), This battle should be your standard/default battle.

Skyfire battery battles could be like a kind of the hill type where you have to capture multiple points to capture the Skyfire battery. If you hold all 3 points, you win. Maybe.. This battle should be chosen by attackers or defenders if one or the other team has alot of EVE support and you want to shoot them.

The Defense Grid could be a straight up Domination match, whoever controls it wins. This battle would be chosen to fight outside of the normal attackable hours if the district battle wasn't won straight up in the first round of matches.

How did I miss this amazing thread?
It's completely unacceptable that this thread isn't blue tagged by True Grit.
OP you've done a stellar job at revamping PC.

Seems pretty damn good but what needs fixing is the lag and player boots, people locking their districts and corps incapable of ever fielding a full team paying to have battles won for them so they can aimlessly farm isk.

Right now pc is irrelevant, no one wants to take part because of this weak behaviour.

If districts would be customizable like you described, the defense grids probably should defend the district for an 8 hour block instead of 16. That way, having more than 1 defense grid couldn't protect a district for 32hrs a day; with an 8 hour block per defense grid, it would would be OK to have 2 defense grids or swap one out for something else and be vulnerable for 16hrs a day instead of 24.

Your proposed PC system is very well thought out. However, I don't think having ambush and skirmish/domination would fit. It would be better to go straight to skirmish 1.0 after the district exits emergency reinforcement mode.