Why would you NOT work towards adding support for the new MIDI stack even though there may still be some edge-case issues with its use (which I think you’ll find are much over-played now). The new stack is NOT going away and is already on every up-to-date Windows 11 25H2 install. The Microsoft team working on it are actively working to address any backwards compatibility issues that they can address inside Windows.
First of all, the majority of users have had no issues at all, and for those that did, most if not all of these have now been fixed over the last few months including the June preview release/July Patch Tuesday as well as by the software and or drivers being fixed by the original developers with the assistant of Microsoft.
The issues that have been shouted about (and amplified by social media) have almost all been for old (often unsupported) software and/or old drivers having issues as they behaved in ways the original stack was not designed for and/or made assumptions they shouldn’t have - breaking the backwards compatibility provided by the new stack which was based on a load of work and analysis across loads of hardware and software. In fact, quite a few of the issues have been because of the significantly better performance of the new stack!
Some very old unsupported software like MIDI loopback tools did some very odd things to work around the limits of 10 MIDI devices in the old stack, and Microsoft has fixed the stack for them EVEN though the new stack has these features built in.
The biggest issue out there that has not been fixed directly has been very old and now effectively unsupported DJ hardware and drivers, where the vendors are not offering ANY support on their side - so, for those people, Microsoft has also added in the ability to switch off the new stack completely and go back to the old one in the June/July updates!
It is also worth noting that using the new MIDI stack will actually avoid most of these issues - as well as opening up support for MIDI 2.0 devices.
To support Windows 10, Cantabile will need to retain the option for users to use the old stack. As the SDK runtime is being included in Windows 11 in the coming months, and the production-ready release (it has already been in beta around 18 months if not more) of the SDK is expected in the next month or so, so this is something that can be worked on ready for its release, as others have been doing for months if not years.
From a personal perspective, I have a complex setup with loads of software including many DAWs and Performance Hosts, a lot of hardware (controllers and synths) and have never had any blocking issues (one small one with WinRT in February with workarounds available), and zero issues at all since March/April — and I now have multi-client MIDI 1.0 devices without third party solutions (removed these now so reduced complexity, always a good thing), significantly improved (around 10ms better) MIDI 1.0 latency on class-compliant devices (which was more than I expected) as well as MIDI 2.0 support (at driver level) for my SL88 Mk2, and MIDI 1.0 and MIDI 2.0 loopback devices “in the box” if I need it.