I suggest that Show-Markdown is an ideal candidate for decoupling from the core code of PowerShell and given a new life as a component in PSGallery. That way it can be developed independently from the core of PowerShell by people who care about it rather than as a low-priority afterthought.
There are many other utilities that convert from markdown to render in a terminal, I don't see the need for PowerShell to duplicate this functionality.