I thought of something that might be enough of an incentive to get folks back into SoF, and for them to stick with it until the end:

Make it so the Tomestones of Poetics that you get from SoF don't count toward your weekly limit.

Yeah, you only get seven tomestones per win, but as far as grinds go it's not so bad. I see that at something a lot of folks would leap at anyway - particularly with folks gearing up as fast as they can for the expansion! If SoF was the only source of unlimited Tomestones of Poetics, people would be lining up for it!