While i like Zpacks, i don't understand what's so special about fleece mitts there, that you couldn't find anywhere else? Fleece is pretty basic and ubiquitous stuff.
Not much difference between a lot of fleece out there, unless you're talking different categories or kinds of fleeces. Picture Bubba from Forest Gump, "you got your micro fleece, your regular fleece, your regular grid fleece, your high loft high void grid fleece, your hollow fiber fleece, your micro and hollow fiber fleece.."
Even most cheap fleece is now pretty durable and pills less. A lot of fleece is now micro fleece to make it feel soft (also increases the insulation some).
If Zpacks ever makes a pair of say Cap 4 type fleece mitts, i'd definitely buy them if they were reasonably priced. As far as i'm aware (not that i've looked much at all recently), not a lot of companies are making mitts out of that specific material, and yes, would be a good liner glove, but only slightly better than the micro fleece.