In fact, this is a very popular feature
It has a good popularity on various websites and forums, and many users benefit from it.
I noticed that this feature is no longer available in RDNA graphics cards, so I hope that AMD will add this feature again
Yes. It is very important. It needs to be revived and OS Wide Support needs to implemented in Windows 10.
It seems to have been developed at the behest of PowerDVD, for exclusive use with their software. Since then, PowerDVD doesn't seem to be keen on supporting continued development of this really cool and unique feature. Good that this feature was added to GCN, and it has been a part of GCN over its generations.
This feature is a really cool feature, unique only to AMD. A hardware video processing filter, part of the video decode block, but using the 3D engine to compute the interpolated frames. Really cool!
BlueSky Frame Rate converter is currently the only was to practically use AMD FMV in day to day general usage. The developer has been able to extract whatver possible, even implementing a 25 to 60 fps conversion feature in it. Which is not there in FMV on its own. But he is doing it alone, by trail and error.
AMD marketing department needs to seize this opportunity, and push their advantage in this hypercompetitive marketplace where marketing has an oversized impact.
With competitors pushing improved video codec support, and AI solutions for streaming(which may be practically limited in actual value to end users), these are huge marketing wins for them. "Mindshare" matters.
This dying and seemingly forgotten feature, is a superb trump card AMD has hidden up their sleeves. It just needs software side support( integration into OS, availability as a processing filter, maybe as a part of HEVC video extensions plugin from Device Manufacturer, available in MS Store)
For Hardware side support, increasing frame rate interpolation range(24,25,30 fps to 60,75,120,144fps), support for HDR and higher bit depth. Reducing overhead and artifacts further(it is already the best in this regard)