If I recall correctly, I heard from somewhere that doing away with PlayOnline would be too much hassle for SE. There's a certain integration between FINAL FANTASY XI and PlayOnline that the friend list system uses. The handling of "Handle IDs" (your identity on PlayOnline, and FFXI) is done by PlayOnline, and doing away with PoL will render Handle IDs useless.

Would be great if it just made the PlayOnline Viewer an optional program we can access alongside FFXI, while FFXI can be gotten to straight from an .exe on my desktop.