If they do VP Hrist, there's pretty much 2 ways to go (well... 3):
Do the story of Hrist before Silmeria was stolen and Lenneth awakened. There's pretty much nothing written about Hrist's active time before those 2 so they'd have free reign to write whatever. The only thing they have to mind is that you need to destroy an entire kingdom at some point.
Do the story of Hrist awakened by Lenneth Creator. This would follow the after the credits foreshadowing of Brahm in VP1 and would be about the queen of Hel invading the other realms.
- Do the VP2 thing again
Make some 'what if' scenario that has nothing to do with anything.
your 3rd scenario makes no sense VP2 is not a what if scenario it directly follows vp1 even though it's in the past. there's some interesting directions they could take with a post vp2 world state.
while theres not much info about hrist's time we know from the einheriar bio's from vp2 that during that time the gates of nifelheim were open and undead were flooding out,and according to the mythos the valkyries are based on hel may be hrist's mother(wich would explain why she's such an obedient try hard). hel never made an appearance in vp2 but was quite relevant in covenant of the plume. if you go this route you could even have Ailyth appear agian.https://www.youtube.com/watch?v=plckmWHU_Dw