We're talking about 1.6 GHz, spread across 2 cores for B&S (Remember, UE3).

The bottom line, in my opinion, is that for the game to Buy Blade And Soul Gold, it would have to be drastically altered and the engine would also have to be heavily modified.
Both feats that would require a tremendous investment on NCSOFT's end. Which IMO, I doubt they're willing to pull.

Similarly, Square Enix did take that chance recently with FFXIV and redid the engine entirely, in hopes of achieving this.

In my opinion, it was successful on their end. However, it is without question that the PC version of FFXIV is still superior to the PS4 and specially to the PS3 version. The UI elements can be accomodated more easily, there is several more options available and I'm not even going to mention things like third party addons.

I'm not talking max.
Max is completely out of the equation here. Average resolution is also out of the equation; PS4 and specially not XBONE will be able to handle 1080P for B&S, or you may need some Blade & Soul Power Leveling.

I am saying the top it will likely go is 720P as noted above (That's being generous).

Your textures could possibly stay at a medium to high level (The memory is there to support it, somewhat) but everything else on settings would go down to medium or less or more than likely, possibly removed completely.

In the end, you would have a not-so-good looking game. Which is why I don't think this idea would be worth execution unless the engine is changed to something else (Unlikely) or the engine is heavily modified (Also unlikely to happen).