If there's anything that Bob won't have to worry about is musical deviation. Who knows if these guys have anything new to contribute, musically, to the act. I remember, years ago, some emails from George where he was pretty torked at Bob for telling him that he could only do old material in his solo spot. I don't think Josh, "Magic Mike," and the other guy (Tim?) could pull off anything close to the caliber of BORN AT THE RIGHT TIME.
I should also note that Bob is very heavy on "aesthetics." I seem to recall postings from Bob Haworth that Shane enforced a "Martins Only" policy on the group around 2000. Also, Bob sort of insisted that Haworth switch to a Tenor Guitar, similar to Nick's. Well now, here you have Josh - looking a lot like his father. Even better!!
I suppose you have another selling point with Magic Mike Marvin. I mean, he could use his vast collection of stunning head-shots from over the years to promote the latest Kingston Trio. And after all, his independent movies about skiing were all named after John Stewart songs...hey, see the additional "Bloodline" here? This guy's been drooling for a KT spot for decades. Yeesh.