I have no idea why people are so obsessed with full frame for this camera. The reason we wanted full frame M-mount rangefinder and full frame SLRs were for only reason because the lenses were designed and made for full frame.
No, that's only one raeson, and valid for people who already have a good stock of such glass; for anyone else, it wouldn't be a reason.
The prime reason is size: larger, as with film, allows more flexibility in any number of areas. What is seen as a disadvantage by some becomes an advantage to others (different DOField, for example), but generally speaking, the more one is likely to be engaging in large prints, the more advantageous the larger format.
Frankly, the only valid reason I can see for not
owning an MF camera is cost as it relates to budget. Even though I would ideally like an M9 for a walkabout camera, that doesn't mean I wouldn't actually be grateful for a larger camera on other occasions. I did use both 135 (35mm) and 120 (6x6 and 6x7) formats in my pro days, and yes, I abandoned 4x5 as soon as my interests allowed, which was almost as soon as I went solo. I currently use dslr FF and cellphone, so what about that as a range? Neither can replace the other for what each does.