I posted this over in the long "new iMac" thread, where todays Mini rumor had poked its head in, but I think it might be useful here too...
Who knows... We haven't seen anything like a "pro-focused Mini" in a LONG time. There has never been an Intel Mac without at least one of the following:
1.) Mobile CPU and Intel integrated graphics (Mac Mini)
2.) A Xeon (or two) (Mac Pro)
3.) A screen (everything else)
The Mini has historically shared a lot of parts with the 13" laptop line, hardly "pro-focused" in a desktop, although the few quad-core models shared CPUs with the 15" MacBook Pro (without discrete graphics). There were certain pro applications where the Mini made a lot of sense, especially when hooking up a box to a bunch of musical equipment - musicians wanted something that would sit in a rack and have a fair bit of I/O, and they generally didn't care about graphics (and the mobile CPU was fine unless they were running a ton of tracks). Minis also made handy little NAS boxes using external disks, and found their way into a lot of photo studios and the like (as well as in software development) that way. The third "pro application" Minis turned up in was in labs (scientists love them for equipment control - tuck it on a shelf and forget it).
Outside of music, the Mini never made any sense as a "pro desktop". iMacs were (and still are) great office desktops - why go screenless in that application? The iMac screen is higher quality than almost anything you'd find in a typical office, and Apple's always given a good deal on the screen in an iMac. Creative applications outside of music generally need graphics in some capacity, and the Mini has always had dog-slow Intel integrated graphics, and has never (yet) accepted an eGPU. The same scientists who use a Mini to control the mass spectrometer generally like an iMac on their desk (or a PC). Software developers probably don't enjoy compiling things on a mobile CPU (although I don't really know a lot of developers, and I've seen how the Mini is used in both art and science from experience).
Apple could go a wide range of ways with a "pro-focused" Mini. Here are 3 possibilities
1.) At the lower end, it could have a relatively decent mobile CPU (either a higher-end quad core or one of the 6-cores) with a bunch of Thunderbolt 3 and USB ports and maybe 10G Ethernet, which would be really useful in a machine that is often a server. Musicians would love it, as would scientists and the "build a NAS" community. Even some graphics sensitive users could find a use for one, with an external GPU. It might well have soldered RAM, and is very likely to have a soldered SSD (remember how much history the Mini shares with the MacBook Pro). This is essentially a modern version of the much-loved previous Mini, although with less internal upgradeability and more connectivity.
2.) If they go to the middle of the range, it might have a 95W desktop CPU, although that is the Mac Apple has always resisted building - it might have Intel graphics only, or it might have a mobile Radeon like the iMac. The last time we saw a "mid-range desktop" Mac without a built-in screen was in the early 2000s, and it wasn't Intel based. I have to admit to being befuddled by this possibility, because Apple has resisted exactly this machine for so long.
It would almost by definition be less Mini than previous Minis (it could have as small a footprint, if it was double height) to cool the CPU. That could attract a lot of pro users, including graphics sensitive users who might use an external GPU. Photographers and video pros who don't find the iMac screen accurate enough and use Eizo or NEC monitors might very well prefer not to pay for the screen. I can almost guarantee that any such machine would be priced to be less attractive than the iMac unless you really didn't want the screen (maybe $500 less than a 27" iMac with the same specs).
If this comes out, they'd almost have to update the 27" iMac at the same time. Otherwise, they'd have a "Mini" that could outrun any other Mac except the iMac Pro. This would be a darned useful machine - almost too useful, because it could hurt sales of three Macs (27" iMac, iMac Pro and the forthcoming modular Mac Pro). Expect next to no internal expansion potential to keep it from hurting other Macs - if we're lucky, we'll get a RAM door.
3.) The third possibility is iMac Pro-type innards in a relatively non-expandable case (probably RAM upgrade only). If this comes, it's a sign that they're aiming REALLY high with the modular Mac Pro. They aren't going to build three Macs with closely related insides at the high end, so a "screenless iMac Pro" would mean that the modular Mac Pro is aimed significantly above it , featuring an Xeon SP or successor for sure , maybe always dual processor. A "super-Mini" might or might not feature the internal Vega from the iMac Pro, because they might assume that musicians and many developers, among others don't care about the graphics, and the graphic arts/photo/video community will always use an eGPU. I could actually even see them using the Radeon 560 from the MacBook Pro 15" (the Xeons don't have onboard graphics, so it can't have Intel graphics) - it doesn't use a lot of power so it's easy to cool, it'll drive a 5K display if you're running Logic or XCode, and it'll encourage eGPU use among graphics types.
If I had to guess, we'll see option 1, with some nice, but mobile (or maybe power-optimized desktop if it's cheaper) innards. If there is a 6-core option, we'll probably see a 27" iMac refresh the same day. Yes, this is a pro machine, especially if it has plenty of Thunderbolt and 10G Ethernet - it's just not a pro video machine.