The idea you want tiering... at home.. just seems so unlikely to save you any serious money, or gain you significant performance.

"tiering" in the traditional sense isn't even popular in the DC with things like Vast, Pure, etc all doing well.

Is there any reason you don't know the data set that is generally cold? The vast majority of home users basically have data that is trivially super cold that needs reasonable read performance - this is just HDDs. Then have a second mount point with things that you need greater performance, and have that be just SSDs.