Perspective, gentlemen, perspective. We scored over 90% of the time with this offense when there was not a serious "human" error [i.e. turnover, penalty] on the drive. Kelly said in a presscon that the staff had shown him the data that they'd scored nearly every time, when you added in the "no seriously negative play" [like a sack, for instance]. In other words, when eliminating the things which have nothing to do with the actual offensive design...The Kelly offense works when the players don't stop it themselves.
As to elite running backs like Isaac: the spread can make an elite RB a star, just like the old, old Detroit Lions "silver stretch" [four-wides] opened the field so much that it max'd out Barry Sanders' skills. [People forget that Sanders had a lot more trouble later in his career when the Lions abandoned that offense for a more traditional set]. If an elite RB wants some very big YPC numbers, something like Kelly's spread will get that for him.
As to the pros: there are a lot more spread-type sets showing up all the time --- very like Kelly's in many ways. One RB standing back with the QB in shotgun, or one back with spread field receivers and QB under center but no FB [we do that a little]. I see no reason why a single back offense cannot attract pro-attention to the player. That RB is required to be good at picking up pass-rushers in that/our offense, and this is becoming a paramount trait for the pros too.
A bigger problem getting recruits at this position right now may be "Wood/ Riddick/ GAIII/ Neal/ Russell/ Mahone" plus the recent Kelly "subtle-shift" to the hybrid "you can't predict where I'm going to be" conception of the RB/Slot. Kelly, though, will be perfectly happy to creatively design the offense around an exceptional skill if such arrives [just as he has now done with 1). Eifert; and 2). the load of hybrid talent.]
My bottom line on the Kelly system, is that I believe that it does not need a 5* RB to make it formidable. It needs a dangerous runner who can utilize relatively open spaces, can pick up the blitz, and catch the ball. Right now that's Cierre Wood's MO. Theo and GAIII seem to be learning the blocking part, so that will be their MO. I'm going to assume that Russell, Neal, and Big Will will get the same three traits downpat, and we'll be loaded.
