What's going on is that CSH having contributed to the Southbank Tapping the Roots last February, the emphasis is on where we go from here: the CSH Choir sang some of Sally Davis' arrangements immediately after the Library recordings to show what can be done, as well as Carthy and Swarb and Flood and Mellon doing free floor slots!
In passing, Pete and Andy are doing another experimental lab using innovative organs (!) at the RFH the weekend of 21-23 March - free floor performance afterwards, I think.

Do you need to stop in the core CS corpus? I don't think so, the idea is to add a record of where we are now: the essence is the English Song element of EFDSS, so it shouldn't be Country & Western, or overly guitar, or, well, anything which isn't fairly mainstream folk - in the sense that broadside ballads made it into the repertoire, so it might be argued that an acoustic version of I Don't Like Mondays could be in the tradition. It's certainly entered the corpus of historical documentation. Of course, CSH will be the determinant.

And then again, there's still a wealth of songs in the archive which are not in the general repertoire. Not to mention the old Ballads, and...