Glad to see you cross-posting this here, crandles. I've been hoping WMC's posts at Stoat would goad Roy into saying something, anything, in the way of a response to Po-Chedley et al. Nothing yet, though.
As for version 6, I can somewhat sympathize ... I've often been a bit, ah, "optimistic" about when I'd be able to deliver something. But not off by three years.
I do like your idea of adopting P-C et al. as the new version 6. You should post that suggestion on Roy's blog. David Appell has mentioned P-C there already, to no great effect.
The discussion of this at SkS was horribly confused. People mixed up the LT and MT issues. It would be great if someone could figure out whether this problem with the MT data will also affect the more "popular" LT data. But that would widen the gap with RSS, not shrink it.
WTF is up with RSS LT anyway?