I've been watching closely for months to see what new hardware is coming out. Today I found a review of the
ZBOX EI750 at Anandtech. It's been out a while and has been reviewed elsewhere before. But it is indeed a Mac Mini sized PC with i7-4770R having HD Graphics 5200. Not a slouch for a Mini substitute. Buy it bare and add your own OS, RAM, and SSD or HDD. $650 at Newegg
I've also looked at the HP ProDesk 600 (starting at $619) and EliteDesk 800 ($699 and up). Both can be configured with as high as i7-4785T. (2.2Ghz, Turbo to 3.2HGz, HD 4600) Nice, compact units as well that accept 2 2.5" HDDs. An M.2 drive is an option.
Brix has a higher power i7 but is loud. One review said it is prone to throttle back due to thermal limits. NUCs are small and boxy but don't have as strong a CPU.
If I had to buy one of the above today it would likey be the Zotac as I could build it out at higher performance/price than the HP.
Looking at Passmark scores, the optional i7-3615QM in the 2012 Mini is no slouch... likely one reason why there was no Haswell upgrade. But for now I'm not buying anything since the new Mini will be out on Tuesday.