I agree with most of what you say. However relying on the old taskbar simply should not be an option. It would be better for Stardock to just add additional support to the new taskbar. Not only would they have to write additional code to "detect" if it "can" use the old taskbar you run into the problem if having to maintain 2 separate codebases. One for when there is the old TB and one for when there isn't. Eventually The first one will simply become legacy bloat code once the old TB is removed however once added to Start11 it would have to remain and be actively maintained for paying customers who have not updated to a "Non W10 TB" version of windows. Otherwise the forums will get flooded with "Why my taskbar no longer works" or "Why do I not have the newest XYZ feature ..."
Pretty much from every viewpoint (developers, end users, ...) relying on older tech that you know will be removed is a nightmare and isn't really required since the option the OP wants can easily (I say relatively) be done w/o using the old TB. My only point was that restoring the w10 TB is nothing more than a stopgap fix that will break code in the "Not to distant future, Next Sunday A.D.)