I would imagine that Rory McC would be a good candidate for a fast long TT. He generates huge power.
If memory serves me correctly, he rode faster than James in #5, but slept in longer!
Then there is Bjorn who rode solo off the front of PBP. Didn't he break the record then?
Doesn't always translate as and some / many / most fast riders simply don't want to do a 24 hour TT and, if they do, there is a learning curve in doing TTs. Even Michael Hutchinson, who has talked about it enough, has never done one!
For example, John Barkman / Veloboy did the 24 the year after he took Gethin Butler's record as fastest UK PBP finisher, and didn't do as well as I expected. Ian To did better but his setup for his LEJOG record showed he wasn't down the learning curve as a time trialist. His position wasn't great and he didn't use a disc wheel - essentially he was leaving Watts on the table. He was trying to challenge Wheels of Fire's LEJOG record but his 24 distance was a good way short.
James, though, is a different prospect. He is a TT rider with fast times for 25 and 50 miles (sub-50 mins and sub-1:45 (wonder what he did in the Hounslow 100?)) so doesn't have a learning curve. However, there would be a lot of pressure on him to do a great ride / get the record, so he wouldn't just do it for a laugh - he would focus on it and do lots of planning and preparation. And it's most likely not what he wants to do, just yet.