Whatever barriers ITX motherboards faced performance & functionality wise are now being pushed aside. One only has to look at some of Zotac's, ECS's or Gigabytes's latest offerings to see that ITX is coming into it's own, not to differently as to how MicroATX did not too long ago. Remember how MicroATX board were seen as a step down form ATX? Here are some links to some vey good ITX moterboards worth checking out. BTW, all newer ITX motherboards, for desktop use at least, use standard ATX power connectors.
GA-H55N-USB3 (rev. 1.0) - GIGABYTE ECS Web Site ZOTAC H55ITX-A-E LGA 1156 Mini ITX WiFi Intel Motherboard
None of these board will allow dual GPU's, personally I run silgle anyways, but other AMD 785G examples would allow for CrossfireX.