Complexity is the enemy of reliability.
I will never ever consider a non-kickstart bike for serious offroad use. I don't care about this "proper maintenance" crap about the e-start systems. They still have problems. Know how much maintenance a kickstarter needs? A torque wrench and some silicone goop around it (or safety wire). Once.
About the only thing the current REALLY YZ450F needs from the factory is a high output stator and maybe a 6th gear. The rest is easy aftermarket stuff.