An external power supply isn't a bad thing. Lumin, Auralic Aries, and many others have external power supplies. Audio Research has done it with their top level preamps. It helps keep the supply noise away from the critical bits inside. It would also be in the same spirit of iFi's previous products which have an external power supply upgrade (iUSB Power, perhaps the most important of their first products for widespread adoption beyond head-fi.) Maybe it will be a (very good) SMPS or maybe it will be a linear supply. My guess is it will ship with a very good universal SMPS, but it will still allow you to easily insert your own excellent LPS (or as they said, a battery supply.) SMPS can be truly excellent, Linn uses them in most of their products, and NAD is using them in their Master Series products.
At any rate, it looks super cool and it may well be enough to keep me from purchasing something else in the meantime. I have been very close to purchasing an Ayre Qb-9DSD but just haven't because I want to see what iFi has up their sleeve. My hope is that the mini iDSD will compete with the likes of the Ayre and Auralic Vega, but do it at half the price and with way more flexibility. I realize this may be a bit unrealistic, but hey I can hope right? Every iFi product I've owned to date (which is most of their lineup: iDAC, iUSB, micro iCAN, micro iDSD, Gemini, iPurifier) has been a very good value. I expect the mini iDSD to be nothing short of stellar.