I can see two opposing economic forces on these items.
Things that will cause the prices to drop:
Introduction of dungeon gear like the claret breeches, alpine jacket, solid scale mail and others are better in their current state than the bucc/harly/temp items. As more people make their way through the darkhold, they will put up their old items on MW and thus supply will rise and price will dip.
As evidence I've already seen bucc shirt prices on Karnak go from 12-15, to 9-10 million a piece.
Also while regional leves are not as effective as before, they are also no longer failed. More players are choosing to succeed, and/or use these for gathering faction, so with an increase amount of faction credits, more faction gear will drop.
Forces that will cause prices to stay stable or increase:
Another viewpoint on the leve changes is less people are doing leves now, and therefore the supply of these items will stay low.
If SE releases any unique materia that will only apply to faction gear, or if this stuff is upgradable, the value will once again go up. Member of my shell and myself have noticed that on the templar gear specifically it looks to have a dull or worn appearance leading to the belief that they will be upgradable in the future.
Conclusion and Suggestion
Faction gear, no matter how you look at it is very very tough to come by in this game for those who don't have the funds to purchase it. You need 600 faction credits to get an initial crack at the NM fight, and 400 faction credits for every fight afterwards, so it's not something you can spam until you get the drop. And the drops are not even guaranteed.
So with all that said, I would really like to see these pieces remain relevant in the game, and for future releases. Please make them either upgradable or buffable via the materia system.
These sets are fasinating and well done. If it is true what they say about a 6 month timeframe to create new gear, it would be a shame to let go to waste 18 months of work, letting because irrevelant.