i have a cutting that is showing signs of top growth but no roots, but plenty of initials.....
pot it into a cup or leave it in the bin w/sphagnum moss?

Very tempting to pot at this point but I would wait til I see roots. You may lose that initial shoot, but that is not as important as seeing roots

I agree with Barry.  Without any root initials, you have nothing to support that growth.

Stevin, you may wish to try my method for a few days before planting in cups, put them upside down, it should force roots to appeat on the other side.  I see the callous forming.      I have a special white greek that arrived here like that, and upsidedown it went, now 10 days later, signs of roots appear and the leaf growth stunted with the upsidedown method.  You are doing fine..those little leaves may die on you...but new ones will emerge, in fact, if you were to plant, I would be tempted to cut those leaves, to force the cutting to grow roots.  

good job there!

You can't wait forever. Pot now and hope for root later, or leave it alone and face mold or rot. But that's not much of top growth. If it hasn't been too long, give it more time. I usually give 4-5 weeks for root initial then to the cup even if there are no root initials, especially if it's rare or more desirable variety.