Use the width axis of variable OpenType fonts

[xscheuer]

This has been discussed on TeX.stackexchange, but I don't see this enhancement feature request here (and then the question was asked almost 2 years ago, the integration and use of variable OpenType fonts has become more widespread, and luaTeX support has also improved).

For variable OpenType fonts containing a width axis (wdth), would it be possible to vary this axis to perform the font expansion?

[schlcht]

As I commented over at TeX.SX:

I doubt that [the width axis of] variable fonts will be usable [for microtype] in the foreseeable future ... it either would have to be integrated into the engine itself (for pdftex, which is basically no longer developed), or the hz mechanism would have to be completely remodeled in luatex taking variable fonts into account.

Though I agree it would be great to have, I have to admit that my luatex skills aren't up to the task.