It's the never ending dream of Mini-fans to get a Mini that is basically at the same power and capability as an iMac but without the screen. Sorry, but I don't think that will ever happen. In fact, given the processors available in the current Mini, and the recently released new MacBook, I think we will see the next Mini in a redesigned, smaller case that shares a lot of the components of the next MacBook update. In other words: the current MacBook will get updated with Skylake processors and such, and the next Mac Mini will probably use similar, if not identical, internals. This means no fan, requiring low TDP. If Apple makes the power supply external, it can be even smaller.
The Mini has, and always will primarily be, the entry level Mac computer, and I don't see Apple changing that ethos.