At the moment that would seem unlikely or at least something we haven't really decided on. Bear in mind our current focus is XF 2.0 and the effort to develop and test an importer is extensive.
Certainly while the adoption of IPS 4 is slow (as it naturally would be between major versions) it isn't likely going to be worth the effort.
If you currently have an IPS forum and you're considering changing in the future, then it might be worth evaluating IPS4 in a test environment and if it doesn't suit your needs, stay on IPB3 until you're ready to move to XenForo.
I have a xenForo forum which we upgraded as a test to IPS4 for a few months. We obviously still have the original xenForo backup when we did this in October, but it'd be nice to merge everything back into one place again given that my members hate the new software (specifically the post editor).
I suppose what we'll do is revert back to October, then leave the IPS4 version on a subdomain as read-only until an importer tool is made - It's only 3,000 or so posts between then and now so thankfully it's a convenience and continuity thing and not something more serious. Lesson learned.