It could actually be a benefit if they (or an authorised third party) offered a DC to DC wiring harness. Having the UPS do one AC/DC conversion, and then running everything on DC beyond that point helps a lot for efficiency.I don't think MagSafe will work well with Mac mini. Considering many of these will be used in server farms, there would be no benefit but catastrophes if someone were to tug the cable a little too hard...
However I have zero expectation that was actually their goal here.