I don't think Apple will choose to make something that is positioned to compete with desktop PCs. Because it has done that in the past (PowerPC series). They were widely criticised back then for those products being un-competitive.
The best way forwards is for Apple to keep the Mini serving the budget users like it is. However a "next gen" Mac Pro tower could easily be smaller more like whats being suggested here. That would inevitably be a replacement of the existing Mac Pro, and not co-exist alongside the old "Mac Pro".
In consideration: This topic really more to do with Mac Pro than Mac Mini, and therefore its more relevant for the "Mac Pro" thread. But for fun here's my take on the...
"next gen" Mac Pro tower
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* Mainly a heck of a lot smaller tower.
* No Dual CPU option. Takes up too much unnecessary space.
* A maximum of 4 x 2.5" Drive bays. For third-party SATA III SSDs. Or 2.5" 7200rpm mechanical backup drives.
* No 3.5" bays. Since that would be pretty pointless these days.
* Between 1 and 2 full length, Double height, full length PCI Slot for Discrete Graphics Cards. In other words between 2 and 4 *single-height*, full-length PCI slots. I wouldn't like to say how many exactly, it depends a lot on other people's views. But 4 slots gives enough space for 1xgraphics + 1pci SSD + 1 other PCI card eg peripheral. I don't believe SLI (dual-gpus) is worth it however.
* No Slot 5.25" for Blu-Ray. Do away with it because those people who need one can just plug in an external one.
* A really clever design may permit sharing between the PCI slots and the 2.5" drive bays.
* CPU:
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1) Mobile i7 Quad core power envelope is necessary for a smaller case.
2) We can ditch the Xenons for Mobile i7's and save the extra TDP headroom for other things in the case - namely a better discrete GPU. After all - its the lack of proper discrete graphics that's the one major defeciency of the Mac Mini.
3) The CPU socket is not missed. The next generation(s) Haswell, Broadwell don't have CPU-interchangable motherboards. Intel continue their integration strategy for the PCH, VAs, Thunderbolty controller and so on. Hence the CPUs are never going to be swappable with each other even if they did have a socket. So being a soldered mobile part is less drawback... At least until Broadwell.
4) However the Mobile i7 CPU will definately have the fastest integrated graphics bundled in it totally for free. iGPU has that Intel QuickSync transcoding engine which people desperately need for video editing. Not only is transcoding faster with QuicSync, its also freeing up the other main components (CPU+dGPU) while doing the transcoding in the background.
I'm under the impression you don't need a mac pro or have serious experience in really using one for its intended purposes. The mac pro is a work horse. You just described a headless next gen imac.