I never understood the aversion to having players be able to buy good gear. In principle we have two resources that we can invest in anything we do, including games: money and time. We all have different amounts of those commodities and therefore value them differently. If SE decided to sell the equivalent of the best loot AND make it so that the gear can immediately be identified as being bought, I would have no problem with that.

The only issue is the price of course. If we say it takes on average 100 hours of game play to get a Darklight body (I have no idea what the actual number is since I don't have the time to spend doing it), how much is 100 hours on average worth in yen, dollars or euros?

But to answer the original question, any system for buying things in game should be on top of P2P in my opinion.