I think you have to 'blame' /'Thank'
Nuance for that development. I believe after all the time spent on his speakerquest with funkmonkey, and Craigsub, he had pretty well settled on the original Songtowers, but wanted that little bit more. Something a little different. He spoke to Jim and Dennis regarding the swap, and they came up with the ST RT. I'm sure he'll jump in if I have it wrong. I think he's addressed what he felt were the sonic differences in prior posts.
As I have no real experience with ribbons can't speak to the difference. I will say my stock STs sound great with the domes, and in my opinion so do my old Dahlquist DCM-7 compact monitors. The Songtowers imaged very nicely from their hookup. Then improved when I added in the DAC, and my listening room would not be considered optimal.
Have you checked to see if there are any SongTowers in your area you can check out ? I'm basically a hermit, but Jim is such a nice guy to work with I took the 'chance' and have met a couple of very nice folks by opening my doors for auditions. If you're going to be up Seattle way let me know, will be happy to set something up.
I am looking forward to checking out some ribbons in the near future. A friend has a pair of Jim's QWs almost completed which I will get to hear hopefully by Turkey Day. In any case, break out that bottle of 12 yr old single malt, or a brew, feed those demons on your shoulders till they relax. aa