While an VSG to RNY revision is possible, there are a number of things to consider -
Is there a problem with the sleeve itself? The sleeve is not standard and with the rapidly increasing popularity of the sleeve, there are lots of bariatric surgeons out there who are just getting their feet wet doing them, so your sleeve may not have been crafted as well as it could have been - if too much of the stretchy fundus near the top has been left behind, you could have more capacity and less restriction than you should.
The RNY, despite its intestinal rerouting, is still fundamentally a restrictive only procedure like the sleeve any malabsorptive effect on you caloric intake is temporary at best (though sadly, its mineral malabsorption is permanent.) The overall weightloss and regain character of the RNY is similar to the sleeve, so there are doubts as to whether a change between the two would help you much. Further, the RNY is something of a dead end on your WLS journey - revising it to something more effective like a DS is very difficult, with only a half dozen or so surgeons in North America genuinely qualified to do such procedures, and if your RNY was made from a sleeved stomach, that would complicate things further, if not make another revision to a DS impossible.
Revising to a DS is a logical step - the sleeve is the restrictive part of the DS to begin with, so such a revision is fairly straightforward, and some would consider it more of a completion of the DS than a revision, and most any of the qualified DS surgeons can do such a procedure. On average, the DS offers better weight loss than either the sleeve alone or the RNY, and is the only procedure that provides much of an improvement in regain resistance relative to the other WLS. Check the DS board here on OH and also check out dsfacts.com for more info and a list of well qualified DS surgeons.
Good luck in your research and further journeys,
1st support group/seminar - 8/03 (has it been that long?)
Wife's DS - 5/05 w Dr. Robert Rabkin VSG on 5/9/11 by Dr. John Rabkin