From the new WSJT-X beta release-notes:
...For those looking even farther ahead: We are well along in the
development of two new modes designed for the LF and MF bands. One
mode is for WSPR-like activity and one for making 2-way QSOs. Both
use Low-density Parity Check (LDPC) codes, 4-GFSK modulation, and
two-minute T/R sequences. The QSO mode reaches threshold SNR
sensitivity around -31 dB on the AWGN channel, and the WSPR-like mode
better than -32 dB...
Interesting it is still possible to develop even more sensitive modes. Wish FT8/FT4 digimodes were not invented. JT65A and JT9 are so much better....
But we can't stand still, we have to go with the flow...