I don't know where to start :-)

If the game is inspired by ODST and it has PKs then maybe it could address some of the story mechanics problems that ODST had...

In ODST we looked for clues and, somehow, finding those "clues" gave us information about what happened to the team mate associated with that clue. The mechanics of this made no sense. The clues were artifacts and those artifacts couldn't give us the wealth of knowledge that we gained by finding them.

But if PKs are in the picture then we could make use of the idea of the downloading and storage of the memories of the dead.

What if a PK could download and store a dead foes memories and send them into the nearest local area node.

What if you eventually find a way to escape from a node? Maybe you are an AI and were missed when your host was killed, maybe you are just very resourceful. You learn to hack into a fallen knight. Maybe they need to be fresh kills when the little soul-flame thingy is still burning.

The first one could be a fresh kill by one of your companions in which case you can help him/her out immediately. Or maybe one gets killed by a booby trapped SOEIV or whatever. But however it works let's say that you can move to a new PK when you die (if one is available).

If there is a large variety of PK forms with different abilities then you have to adapt to your current shell, what it can or can't do compared to other hosts. So if you "die" in combat and a soul-flame is near then you can resurrect the PK's body and take it as your own. If there are no flames then you revert to checkpoint.

You need to find out what happened whilst you were "dead". You search for your companions, find their souls and relive their deaths.

You piece together the story (whatever it is), maybe you find a way to reskin your allies - give them back their bodies or download them into PKs.

I'm just thinking out load here. There is a mythic theme of a hero descending into hell to bring back loved ones. This isn't Dante's Inferno, it's an older theme. Maybe you could get a game story out of it.

Anyway, I just thought that I'd share...