i think a trusted voice will deliver his thoughts on this quandry shortly ;)
i've been humming and hawing something similar:
http://www.planet-x-usa.com/product-p/buoofat.htm
on one fatty rolling chasis - frame, fork, wheels and tires - for $880 (plus shipping). front end is trail-slack, and the fork is suspension correct for ~100mm of travel so you don't have to commit to rigid:
looks pretty shred-able :)
Did this last winter, built it up with lots of spares. Over a couple months, swapped on a carbon fork, a Hope/Surly new rear wheel, and drilled the front rim. Swapped in some way lighter q-tubes.
The stock fork is really, really, really heavy. The rear hub is really, really heavy and crap quality. The tires are pretty good though. The tubes are boat anchors.
IMO, the frame alone is worthwhile, but the rest of the parts are really meh. Get frame, build it up with other stuff.
It's had more dirt time than snow time. It's really fun, and I'd do it again!
When I want a hardtail ride, this bike gets picked over (gasp!) my Chromag.
Hell, if I didn't already have both, the idea of one of the Chromag fattys with a Bluto and two wheelsets…