I would love to see him just run something the out-of-the-book Pfitzinger 18-week, 100MPW (or even the 85 MPW honestly) plan for his next road marathon. I guarantee he'd crush his past times with the additional speedwork and the additional time he'd have for recovery not fooling around for 140 miles at a pace so slow he barely has a pulse. It'd also make for a great 4 months of vlog content as he documents it all.
I said Pfitzinger, but it can be Daniels, or Hudson, or a higher-mileage Hansons plan. Anything more structured and systematic than the homebrew monstrosities he's ran the last couple tries. Something based on an accessible book that people can go out and read and follow themselves and relate to.
Personally I think he has a better knack for the mountain running stuff, but if he's hellbent on the marathon I'm in on watching him give it a go at training properly.