So I'm a ReactOS fanboi, but... but...
- You need to fix your flaccid dev community. Your forums have a terrible S/N ratio. IRC may be great and all, but I don't see any hard documentation behind any design discussions or development. I do see crazy shite like "can I run ReactOS on Playstation 2". The forums make your project seem dead, which it clearly isn't.
- You need to fix your flaccid dev community. It needs a larger presence. It needs to be tangible (who is doing what? who are the people? do you have conferences?)
- You need to fix your flaccid dev community. There is a bunch of really useless, out-of-date, confusing and out-right self-inconsistent information on building ROS, and the Git move didn't help (but kudos on the move, it is long overdue). I've tried 4-5 times to do something, but the directions I followed on Win, Ros or Linux all ended up breaking somewhere.
- You need to fix your attitude problems (or your forums). There are people asking reasonable questions, who get actively or passively aggressive answers. Not good.
- You need to fix your toolchain problems. This whole SEH thing is getting out of hand. Does Clang support SEH yet? It might - https://clang.llvm.org/docs/MSVCCompatibility.html. So maybe you need to bail on GCC, or maintain your own fork of it (yes, it's ridiculous that GCC still doesn't have SEH support, and the patents have long expired).
- You need to get a grip on x64 support. Your toolchain problems cannot be a gate (and you can clearly use MSVC for building... so...). IA32 support is great and all, but needs a back seat to x64.
- You need to get a grip on UEFI booting (note UEFI booting does not /necessarily/ mean you need improved ACPI support, in practice)
- SMP?
- Forget Xbox, NewWorld PowerMacs (those were BE anyway) and 32-bit Arm chips (which outside of the Pi are too varied and too few). Targeting 64-bit Arm chips does make sense, though, now that Microsoft has released a client build of Win 10 on laptops and an Arm server vendor demoed Windows Server at OCP'18 (http://www.opencompute.org/assets/Uploads/18150J-Ampere-PPT-...). You will need UEFI and reasonable ACPI support to support ARM64. You can target SBSA and SBBR compliant systems and this will give support for the entire server ecosystem (and qemu VMs, har har).
- You might wish to minkernel-ize ROS as well, so you can boot without a GUI.
- You might wish to update Wiki (and build a list of links to relevant pages) for active subprojects.