...Only experienced luthiers in Taylor are selected in making these fine instruments (10 years at least). But what are the major differences in terms of build and design that separates it from regular Taylors? ....
Each one of the RTaylor team (five, IIRC), were completely adept at fully building a fine guitar on his own, yet within the RT team functioned as the "specialist" of one aspect of the build. So you had one guy who was the killer inlayer, another who shaved the tops just so, and so on ...all with the hope to allow the best to do what they do best.
One of primary differences in build is the solid lining. Production Taylors have a "kerfed" liner whereas RTs are solid (look at the current Builder's Reserve guitars: solid lining ...gee, guess where that idea came from?

). The solid lining allows a stronger structure which then allows them to build it lighter for better resonance and "livlier" tone, yet maintaining all the strength and rigidity a guitar needs to last. The analogy is like that of a race car where strength and paring down weight
must go hand in hand if you are going to end up with a final product that truly performs.
And in engineering (as layman hack but die-hard gear head bleeding oil/gas since a wee little lad, and still involved in amature racing to this day), reducing weight in one area allows a reduction of weight in another. All of which for the express intent of increasing performance, of course. Follow this to the next logical step and weight comes down across the board, strength is retained if not enhanced, and the window potential for increased performance opens wider. So as opposed to production-line Taylors, tops are thinned, braces shaved, each aspect that affects tone is labored over ...not unlike adjusting the spark timing a degree here or there to gain even the most modest single increase in performance because
all told, each individual enhancement cumulates into a winning machine.
OK, all that sounds like ad copy, I know. But I'm no kool-aid drinker, and I have had my share in the past of buying into the snake oil, only to be disappointed when the goods failed to meet the bar the marketing verbiage promised. Which is to say I grew up, grew objective, and learned something about discernment. In sum, my cheesy way of saying I love R-Taylors
over Taylors that I love. The latter are IMHO the best
production-made guitars out there ...choose whatever tone you prefer, but in terms of build, performance, technical advancement, and overall quality, Taylor builds production guitars like none other I have seen; while the former are truly luthier built guitars built with individual craftsman's time and attention paid to every build detail that the highly-touted boutique builders instill in their fine products ...yet all with the backing of the mother ship.
So the R-Taylor is no "gussied-up" Taylor. It is different from its production counterpart from its very conception. RTs really do sound different. They really do resonate/vibrate more against your body. They are physically lighter yet purportedly stronger (I ain't hacking away at mine to test this one

). And every aesthetic detail is poured over, and their time spent is in clear evidence everywhere you look.
Only the individual can decide if the cost difference is justified: that's not my intention. I'm just responding to the OP, and all IMHO of course. I can only hope that RT will return to work its wonders, but only for personal bragging rights and satisfaction as I can never afford to buy one new. But even if they never come back to the marketplace, I will continue to rest in the satisfaction that the RTs I own are the best guitars I have ever had the pleasure to play and own. None of which diminishes Taylors one iota as much as it declares RT in a class among some of the stellar luthier-built guitars out there.
Edward