I'd best let the fatbike afficionados answer that but I'm guessing the simple answer(s) is: a/ fatbikes are good/fun for snow/sand, b/ something different anyway, and why not eh, but c/ as many on Here will say: it makes little difference WHAT bike you have, you'll still be able to "bikepack". As Stu, myself, and some others would witter on about - it's more of a philosophy than a bike/bivi/tour thing. Then again many would disagree with us. And there's the fun of it! Personally I usually ride my 2007 Orange P7 - it's unfashionably 26", has 3x9, front suspension, and most importantly - I like a nice, cold, hard, piece of steel between my legs
. Then again I, and others, have successfully bikepacked on a Brompton, and some have even used unicycles
Summary: use whatever bike and kit (while still "suitable for the weather" obviously) you happen to have already, and you'll still have a blast.
Then tell us all afterwards, w'd love to hear about your adventures
"There comes a time in your life Ponsonby, when you think: 'My God, I'm two-thirds of the way to the grave and what have I done?" - RIP
"It is in the petty details, not in the great results, that the interest of existence lies" - JKJ