One angle I haven't seen explored is a Loyalist successor of the Word Bearers…

I am imagining all sorts true faith powers that make the Adeptus Sororitas look like Unitarians. 

 Of all the traitor legions, the Word Bearers are probably last on the list of Legions that the Imperium would resurrect. Arguably the first to fall to chaos, and never particularly effective (in purely military terms) in comparison to other Legions, I just can't see a reason why the Imperium would bother.

Apologies for sounding so negative, I'm not trying to pour scorn on the idea…I'm just doubtful that the Imperium would need to use any of the stored traitor geneseed, really. Even if you run with the concept of Berserker Chapters, I can't see the Word Besrers "bringing anything to the table" that couldn't be handled more effectively by either Loyalist or other Traitor Legion geneseed. 

Their particular strengths were religious fanaticism, the ability to (slowly) convert people to their cause and their numbers-they were one of the larger Legions. None of these strengths really suit a modern Imperial chapter. Religious fanaticism is now a given, Chapters that proselytise their own chapter cult would get into trouble with the Ministorum, and chapters that proselytise the Imperial cult would be deemed by the Administratum to be tools of the Ecclesiarchy. And chapters are (theoretically) restricted in size, defeating the principle asset of the original Legion.

I agree that it is implausible.

Iirc a possible reason that Blood Ravens/1k Sons exist was the 15th's fleet were ordered to disperse before the SWs invaded the Prospero system. All the 15th stationed on those vessels would be saved and still loyal. Only a faction of the Legion, but perhaps near 1000. If they fought the traitors heroically during the HH, they might have been pardoned and given a new identity by the new lords of Terra, who needed every loyal SM they could find.

It is implausible that any Traitor geneseed would be used for new founding. However, as a 'what if' the Word Bearers is an interesting one.  Lorgar turned to Chaos because the Emperor spurned his worship. Lorgar needed to find a higher power to worship, and they introduced themselves… A modern Word Bearer chapter wouldn't have this issue and all the potential in their geneseed would be unlocked. I.e. True Faith powers.

Lightbringer said:

Damn, that don't sound very well because I have two Chapter ideas who are pretty close with the Ministorium.

 I'm probably exaggerating the extent of the potential issue. There are (informal, historical, messy and slightly incoherent) checks and balances built into the Imperium's political systems. There is a secular power block (the Administratum) and a religious power block. (The Ministorum.) My point is that any marine chapter that gets too cosy with any one of those power blocks will piss off the other. A bit like the USMC getting a bit too close to the Mormons. Marine Chapters are expected to stand aloof from these things…( not that all of them do.)

Lightbringer said:

Yes, that sounds more in line with what I was imagining. One of them are Emperor puritans who have renounced their own progietor and exists only as the "sons of the Emperor" while the other is more mystical in nature with a alot of cooperation with the Ecclesiarchy since the Ministorium helped them out at a time when the Chapter was pretty deep in dirt.

Having said that there are plenty of documentaries canon chapters with string ties to the ad-mech, whose faith would be considered nothing short of heretical if it weren't for the Terran/Martian treaty that allows them to continue their worship of the omnissiah