If I was looking for a simple, reliable QRP SSB rig for HF use in the coming years then the Hendricks QRP Kits version of Ashlan Farhan’s BitX transceiver for 20m would be in the frame. They also do a version for 17m, but there is more chance of QSOs on 20m. The rig has a useful 5W pep output and looks straightforward to build for most people. The Ashlan Farhan design is well proven. Going from 100W down to 5W is only just over a couple of S-points. 5W will get you plenty of QSOs on 20m SSB. 5W is fun.
A 10m version would be fun, but sadly is not available, but likely to be less useful in the years to come, apart from summertime Es. A 10m design would need better MOSFET PA devices anyway I think.