I thought Jeff confirmed this for 2017, I have been asking him on twitter but alas he never replies.
I seem to remember reading a quote to the effect of "we're working on getting T4K out this year, then getting Polybius out next year".
He doesn't seem big on committing to release dates. At one point PC Gamer quoted him as saying Polybius' PC release would be 2017 once the PS4 exclusivity period expired, but now T4K is a thing it's been pushed back to 2018. Weh.
Jeff Minter is still around? He was making titles for the ZX Spectrum in the 1980s, so I'm interested to see what this is.
Minter's been trucking along making games ever since. You have some good stuff to catch up on if you haven't played Polybius, TxK, Gridrunner++ or his other recent work!