well, i'm not saying its impossible, just saying it'll take alot of work and modding. ITX cases generally have a hard time fitting not just the rads but other components like res and pump as well. it'll take some modding to make room for those components. it also depends on the size of the itx case. a mini tank is "almost" an mATX sized box so at that point, you should ask yourself should you stick with ITX? or maybe move up alittle in size and get a TJ08-E for superior cooling and flexability? not all ITX cases need to be small, (heck i'm using a FT02 with an ITX board
) but the question comes down to the reason for the ITX to begin with. personally i like ITX form factor due to it's flexibility in future re-purposing. (I intend to make my existing rig a HTPC when I move to Ivybridge) and ITX is the perfect form factor for that re-purposing. ITX board fits in ANY case on the market today since ITX is an ultra minimalist version of the ATX standard.
what it comes down to is, if you use ITX for it's intended use (minor to no OCing) it's a perfectly good form factor. however, if you intend to go HEAVY OCing, then you really shouldn't be using the ITX form factor anyway because current generation computers are GPU bottlenecked anyway. even if you put a 7990 in the system, you still wouldn't need to OC the CPU to use that card fully. and that IS the ultimate limitation of the ITX form factor since it only has 1 expansion slot.