Size specific designs are (luckily) more popular and talked about than ever before. Users as well as type and software companies are discussing how the use of different design variants can be made easier and more intuitive, or best even automated, so that if you set the typeface in a certain font-size, the appropriate optical size designed for this size range is chosen automatically.
In theory, this is a great idea. But the problem I see is, you can’t take the point size specified in the document as the only reference to determine what the ideal optical size to use would be. What if the user is setting a sign intended to be seen/read from further away? Or a poster, or boards for an exhibition? He might choose a large nominal point size which then prompts the application to switch to a deck or display variant, but the actual piece will be read at considerably larger reading distance = perceived in a much smaller size, more comparable to average body size at average sofa conditions. How to factor this in in an automated system? Minutes of arc?