First, does Logos still own the copyright to the SBL GNT?
If so, I'd love to see the apparatus updated. (For those who haven't seen it, the SBL apparatus is different that NA28/UBS/THGNT etc. It cites variants by the Greek text rather than by the manuscript. In other words, instead of citing A, B, 0219 (and so forth), it'll cite NA, TR, WH, NIV-text, etc.
Here's a SS of the NA28 apparatus at John 5:3-4-

And here's a SS of the SBL apparatus at the same place-

You can see more variants in the NA28/A, but you can see how the primary Gk texts handled these in SBL (RP=Robinson/Pierpont, the 'majority' text; WH=Westcott and Hort; Treg=Tregelles', etc. The TR and the NIV base text are also cited where they differ.)
The problem is, SBL need some updating. It has neither the text behind the NET Bible nor the text behind the LSB, and both are becoming very popular (and both handle the majority text/critical text a bit differently). Probably should wait until NA29 is released, which will have CBGM for the general epistles, Mark, Acts, Revelation, and hopfully John.
(...and BTW, adding Comfort's NTTTC to a layout will show you which English versions publish the variants in the text itself or in a note or margin.)
Any chance Logos will have an update done at some point?