Update: ArcaOS 5.1 has resolved these issues, and DOS-based BBS doors work as expected, and performance in general for the DOS/Win3.1 subsystems are greatly improved. Kudos to the dev team for fixing the only real set of issues I had.
ArcaOS is the successor to eCommstation, which is the successor to OS/2 Warp 4.
Or, at least, that's the marketing presentation. It supports much more modern hardware - SATA, a good VESA driver for most video cards, and more or less support for every sound card you could care to name, and maintains support for the OS/2 software library.
I say "most" because there are some issues in ArcaOS around the DOS and WinOS/2 support that are complete dealbreakers and make it, unfortunately, a poor replacement for what someone just fiddling around with OS/2 is likely to want to use it for.
The root of the problem is that OS/2 is from an era where you could expect proper BIOS support and that your BIOS would fully implement the original PC BIOS specifications, and that your video card would be fully compliant with the VESA standard.
Unfortunately, you can't expect this on new hardware, or, for that matter, any hardware going back into the last decade, which leads to some broken functionality.
Modern UEFI has a BIOS compatibility layer that may or may not be a good compatibility layer: it's usually just enough to boot Windows 7 and because that's the only thing that needed the compatibility layer, which led to essentially no motherboard manufacturer willing to invest in the cost for a full specification BIOS layer because essentially nobody would ever use or need it.
Worse, you also can't count on any recent GPU to fully support the VESA specification; your modern GPU probably supports most of the specification and it probably works, but there are zero guarantees any given card will be fully compliant. ATI cards seem to be more likely than Intel integrated graphics or nVidia cards to support it, but you'll still have to look back at least a decade or more for anything resembling full support.
These two issues led to a situation where the DOS virtual machine was broken on the 5 systems I attempted to utilize it on - I was going through my old closet junk and seeing if I could utilize ArcaOS for a BBS project I had gotten tired of fighting 25-year-old hardware and OS/2 Warp 4's less than modern creature comforts.
The unfortunate behavior is that the DOS implementation would simply display two characters in the windowed-mode DOS session, and while it was "responsive" to input, it used 100% CPU and was effectively unable to run any programs - this was, by itself, a complete dealbreaker for the BBS project because OS/2 based BBS software needs a working DOS VM, because essentially every door game and most utilities and support applications are DOS-based.
I kept trying older and older hardware in hopes that, once I had figured out why it wasn't working, I'd eventually find something old enough that this issue would resolve itself simply due to the age of the hardware I had selected.
But as I had no luck with any of the available hardware and without working DOS it was a dead project.
I then installed ArcaOS on a Haswell-era G3258 Pentium and was seeing if it was usable as a more modern Windows 3.1 and OS/2 platform, and even then, it was a bit of a failure there as well.
The Windows 3.1 session does work, but the performance on the dual-core 4ghz Haswell was worse than Windows 3.11 on my more "daily driver" Windows 3.1 system which runs on a Cyrix 486DX2-66 and is substantially more unstable than it as well.
This, again, appears to be modern hardware interacting with ancient drivers and hardware assumptions resulting in an unusable platform.
As for how native OS/2 stuff runs on ArcaOS: it's stable, and fast, and the updated driver support, updated installer, the inclusion of lots of community software and packaging tools, as well as the addition of things like SMB file sharing and remote desktop access makes it pleasant to use.
The problem, is, unfortunately, there's not any reason for your random retro enthusiast to care about OS/2: there are essentially zero games for the platform, and the software library is substantially smaller than DOS/Windows 3.1 and what software that does exist is not especially compelling after all this time.
This, of course, is also what likely killed consumer adoption of OS/2 originally: there's no special software, and sure, while you can run all your software through the DOS or Windows compatibility layers doing this was more expensive than doing it natively because OS/2 had much much higher hardware requirements and that meant it was needlessly expensive to run if you had no OS/2 specific use case.
So, in the end, It's a product for people who have some embedded OS/2 application somewhere they just cannot replace with anything else and allows them to use their old software or hardware on a newer system without having to try to figure out virtualization (which, by the way, works pretty well with ArcaOS and VirtualBox and essentially not at all with OS/2 Warp).
While it was a fun experiment, I think I'm going to keep the Pentium 3 I've got OS/2 Warp 4 on around and likely will repurpose the ArcaOS system for some other project.