Again, I think the adjustment to UTMB for a runner like Kipchoge would for sure be "harder" than a course like Javelina or Western States.....
but I won't think he'd be sitting and weeping by mile 30. He might not win the first time around (Even Jim was "only 5th" or so his first time, but Jim is also "only" a 2:15 marathoner). Sure sometimes the 2:15 marathon guy loses to the 2:25 guy in these ultras but generally road marathon times and fitness correlate very, very well.
As far as E. Africans showing up at Comrades....well I know from personal experience of running on "elite clubs" at Comrades they often like to limit how many top E. Africans they let on to the teams and into the race (because they'd rather have a South African run and win). Generally the types of guys who win Comrades are already sub 2:20 kind of runners though....if not sub 2:15. There have also been major doping issues at Comrades...but that's a whole other can of worms....
I'm not sure what your point is here exactly? I already went over why it's not financially lucrative for a 2:05 road marathoner to switch to ultras. I also went over the fact that a lot of top E. African Marathoners probably have no idea about events like "UTMB" and "Western States" or "ultra-marathon trail running." Just like they don't know about "skimo"
It's not about the race prize money...it's about getting a contract with a salary and travel budget and bonus structure. For some it's about "social media attention" and being a "mountain athlete" and running in some of the most beautiful places in the world.
Generally the people doing well at ultras still are middle to upper middle class to wealthy white males in the age range of 25-40. It's for sure a niche sport. But for someone like me coming out of Hansons with a 1:04 half and 2:16 marathon PR it was for sure way, way more lucrative than staying on the roads.
And finally, I really don't think UTMB would bend and let Kipchoge in. They certainly didn't for Kilian (he still had to run a qualifier every year). I think Kipchoge could easily qualify and get a top 3 at the first ultra race he tries though and establish a UTMB index and gain entry easily though. Western States would also very likely not let him in automatically unless he got in on a "sponsorship slot"....otherwise he'd have to qualify with a Golden Ticket or lottery entry like everyone else.