This is huge for people who have found themselves capped on one or another of these currencies for a while now. I know for myself, I've ended up stockpiling heirlooms for characters I may or may not ever level just to keep below the JP cap. Now I can get serious about those last few PvP items I've been holding off picking up. I am surprised to see a valor-to-conquest conversion but not a conquest-to-valor one -- seems somewhat unfair, as it gives PvE players with access to a lot of valor points a way to jump into PvP but gives no such return for PvP players who want to get a leg up in PvE.
Keeping in mind it's the PTR and is always subject to change, of course, this should be a more interesting solution to point capping than we've seen before with trade goods and suchlike.
WoW Patch 4.1 is on the PTR, and WoW Insider has all the latest news for you -- from previews of the revamped Zul'Aman and Zul'Gurub to new valor point mechanics and new archaeology items.