These plugins will be added to Studio 2 as per the roadmap and as is in Studio 1, it will appear in the future maintenance releases.
Also previous plugins will not be enhanced but, as has been previously done, support for newer Operating Systems issues will be taken on a case by case basis. So your primary concern about DeNoise 6 will be addressed in the update to support plugins.
Any other talk about supposed “direction of Topaz” is simply conjecture unless it comes from Topaz Labs officially … third parties simply have no idea. Topaz continues to add functionality, such as batch processing, RAW demosaicing etc., etc.
For those wondering about Topaz Studio 2 and Topaz Labs direction you can find the FAQs here.