I’ve only found one reasonable example of a imperfective future in the dozen or so grammars that I have.
Philippians 1:18 – And I will continue to rejoice.
But it must be asked, if this is the only example (and every grammar I’ve dug provided no other clear example. These include Porter, Fanning, McKay, Campbell, Burton, Roberton, Moule, Moulton, Goodwin, BDF, Turner, Wallace, Zerwick, and Nunn.
And Philippians 1.18 does not necessarily need to be imperfective in meaning. It may very well mean “And I will rejoice [as I should]” with the sense of intentionality that is at times found in future forms (because the future historically came out of the aorist subjunctive).