Thanks for this question, it really makes me examine my "wants".
1) I get a QB under center from the DC Wing T. I have coached 9/10/11/12 and if I am honest, we have a gap at the traditional QB when we hand these kids off to the MS. They are playing catch up with our group. We have been single wing almost exclusively and to have to teach the basics to a prospective QB has to be daunting. I want to go under center for at least a portion of our offense so we are getting QB's ready for the next level.
1a) I get a bootleg/keeper game that I don't get from the single wing. I love the simple snap of the single wing and the straightforward power game with some misdirection. However, one of the biggest plays for opponents last season was the bootleg. I have a great kid to run this with, he was my 2 back in the SW. He will thrive on the boot and on the QB wedge.
2) I don't know that I especially like the plays that open with the reverse pivot, I just know the vast majority of wing t plays do.
3) Finally, I was avoiding the under center wing T because I didn't want to put that pressure on my QB and frankly use that much time teaching it. However, I spoke with his dad, an AC for me last year, and we are gonna start meeting once every week or two to work on the RP, the terminology, and the passing game. I am thinking if he is way ahead of his peers then he will feel less pressure.
So, look like I will be breaking out my old DC Wing T install videos 
So what you have is a mixture of pedagogic and strategic/tactical reasons. There are certain things you want to teach (deliberately giving players more to learn), and then there are certain things you want to do to make things easier for you and/or your players.
When I was thinking it might be a pure strategic or tactical consideration, I was thinking of any of various sorts of hybrid formations that give you the advantages of someone under or close to snapper but also allow you to snap deep. Lots of ways that's been done, positioning a QB-BB sidesaddle (my preference), or with feet spread to snap thru, or able to reach under center from slightly to the side, or a short distance away to get an angled snap. He's a ballhandler when it's snapped to him, a blocking back (or possibly pass receiver) when it's not. Examples of such offenses are sidesaddle T (considered a version of single wing if the snap to the QB is de-emphasized), Howard's modern short punt, Bruce Eien's current FAT, some types of double wing I saw on Long Is. in the 00s, and Sigourney-Keota's single wing. If you don't like reverse pivot, well, for instance, Howard's modern short punt has practically none of that.
However, if you're thinking not so much tactically but in terms of teaching a position with skills that might be useful in other offenses, you'd be better off with 2 packages with someone as a HB in one becoming a QB in the other. From your considerations 1 & 3, it looks like you don't want your single wing blocking back to learn "quarterback skills", you want your tailback or fullback to do so.
In terms of pistol wing T, an example of an offense with that kind of flavor was The Saint Offense, the videos of which may have been taken down. It was a concoction of a HS coach in Nevada IIRC, and the QB and TB were almost in a line behind center, but with enough daylight that a sharp snap was able go deep comfortably without the QB's having to dodge it. Lots of waggle & bootleg plays in that.
