I've not thought about this before, but it's a good idea. My initial thoughts were that working out how ghosts, undead and Yuan-Ti would be the three most important areas to check.
I think the problem with this sort of thing is that both psionics and Ghostwalk are "optional rules", rather than core rules, and WotC didn't make a ton of support for tying various different optional rules products together. (It was mostly "Option A + Core", "Option B + Core", "Option C + Core", etc.) But it might be possible to infer how the different rules might fit together.
There are plenty of Psionic Rules in the SRD that could be trawled over:
- Races, Classes, Skills, & Spells
- Psionic Feats
- Psionic Powers Overview
- Power List
- Psionic Powers
- Psionic Items
- Psionic Monsters
- The duergar (psionic dwarves). I don't think they would be based in Manifest, but it should be possible to stick a duergar city under the ground on the Ghostwalk map.
- The Eidoloncer is probably not a good fit for the psionic Classes (and Prestige Classes): It might need to be modified to create a new "Eidolonpsion" class,
- Autohypnosis: This Skill might have some use for ghosts or against ghosts.
- Ghost Attack: This Psionic Feat is probably going to be something a lot of PCs might want to take. It would be a real game-changer.
- Shadow Body: This psionic power might get used by a ghost. You might need to make a call on what happens.
- Ectoplasm: There are a lot of pages dealing with ectoplasm. That has an overlap with the Ectoplasm from Ghostwalk. Looking at that is a must. Either the Astral Ectoplasm needs a new name or you need to decide that both Ectoplasms are the same thing (in which case this becomes a fairly major thing).
- Ghost Crystal Anchor: This probably wasn't designed to work against ghosts. You might need to rename it...or make it work against ghosts.
- Psychoactive Skins: These might be useful to ghosts, as they are made of Ectoplasm.
- Undead Psionic Creatures: This would be undead, rather than ghosts. This would be a fairly important thing to deal with.
There may also be some psionic rules that are not in the SRD that would fit well with Ghostwalk.