That's the rub right there. SE would have to be FAR more consistent in their PvP updates for this to work.
I agree that it would be nice to be able to use Wolf Mark Gear in PvE, because one of the bigger concerns I had when queuing for Season 1 of Feast was splitting my time between farming up-to-date gear in PvE content as well as trying to get the occasional match done in Feast. The problem is that, currently, SE only puts out one PvP set for every two or three PvE sets. A sanction wouldn't balance correctly with current PvE gear within the full term of a major patch cycle. In the early stages of a patch cycle, PvP gear would sync higher under a sanction than most PvE gear; whereas, late in the patch cycle, it would be much weaker, as SE wouldn't have provided an updated PvP set to keep pace with newer raid/upgraded tome gear. If they were going to do this, it would almost be better if they just dropped the "PvP" aspect of the gear entirely and just made the PvP sets another viable option for gear farming (similar to crafted gear). That could potentially work if the PvP set was given and adequate upgrade to keep pace with Raid/Upgraded gear late in the cycle. The upgrade would also have to be a pretty lengthy grind to get, otherwise PvP players would be outstripping Static Raids Parties in terms of how fast they upgraded. That said, this could work into an upgraded vendor system quite nicely, so long as the PvP vendors provided adequate materia for fusions.
Regardless, even if they did do this, it still wouldn't quite feel right, because it wouldn't really do anything specifically related to PvP content. At this point, I'd still take this option over nothing, because nothing is what we have right now, but I would still have liked to see PvP gear provide at least some type of advantage in PvP content ... Though, that may be impossible. Even with minimal stat increases, people cry about "unfair" advantages; so, I doubt SE would be able to do anything truly PvP related without getting a lot of unjustified backlash from the community. It's really sad, but replacing Morale with re-spec'd PvE gear may be the only viable option that we have in terms of PvP vendor gear.