Can't remember. Do aftermarket AT cases take pc/xt or baby-at motherboards? I believe they're the same thing.
There were plenty of aftermarket AT cases that took full-size AT boards; many early 386 and 486 motherboards were the extra few inches wide of the original IBM AT. Even some relatively small footprint desktop cases could take them. (I used to have a compact, but fairly tall, desktop case that originally had a 386/40 motherboard in it that could take a full AT board; it could do this because its power supply was physically much smaller than the ginormous one in the 5170.) Cases that take XT-size boards were called "Baby ATs"... and yes, by the 90's the full AT board *had* pretty much died out so many of the "AT" cases from then were actually baby ATs.
(If you look through magazine ads from the mid-1980's the term "baby AT" was sometimes applied to Turbo XTs that happened to come in cases styled to look like an AT, and that may actually be the origination of the term. IBM's 5162 XT/286, even though it *wasn't* styled like a "baby AT", may have actually contained one of the first "baby at form factor" 286 motherboards. Very few cloners actually followed IBM's lead in putting 286 motherboards in XT-styled cases, however, they already had their looks-like-an-AT cases to shove the boards into... which probably was the right choice when it comes to customer confusion.)
I have vague memories of full AT form-factor Pentium Pro, and *possibly* Pentium II motherboards(?) being a thing, but they're rare as hen's teeth. Those would be the last examples of the full AT form factor.
Per the original question: I wouldn't mind having a 286 if someone gave it to me, it would be an interesting challenge to try to make a RAM card for it (ISA bus sizing is a fascinating subject, and I even wrote some GAL code and tossed together a draft design for an extended memory card, but that project fell behind the sofa in part because I don't actually have a 286) and it might be fun to play with some of the more obscure examples of software/OSes that run in Protected Mode (the holy grail is probably the abortive attempt by Digital Research to make a 286 version of Concurrent DOS; that only runs on certain revisions of the 286 chip because Intel kept changing some undocumented instructions out from under the DR developers). But the blunt fact is that most 286s spent the majority of their lives acting as fast XTs running Real Mode software (which they ran fine, but too fast for some old XT-dependant games), and the only protected mode OSes with even a modicum of software available for them (OS/2 1.x, Windows 3.x) came out so late you need an unusually maxxed out 286 to meaningfully run, and unless you have an unusually fast one they seriously chug. (And in the case of Windows 3.x you're missing out on things like DOS program multitasking that you'd get if you ran on a 386 instead.) So, yeah, I think the argument that 286 ATs are simultaneously "too new" and "too old" holds some water.
If you could only have *two* computers I definitely don't see making a 286 one of them, a Turbo XT (or Tandy 1000!) and a 486 with an 8mhz Turbo switch would cover about the maximum ground between 1982 and the early-mid-90's. A 286 just cuts off the start of the spectrum without adding anything unique. (A 486 at 8mhz will perform about like a 20mhz-ish 286, should be mostly okay running all the software a 5170 can run well.)
