Yes, some do instruct on a PPL.
1. Those who cannot hold Class 1 medicals, but just enjoy instructing.
2. Those who have military exemption from some of the CPL exams, but don't want to bother with the cost of the CPL when they're happy to do a bit of part time instructing.
You can expect a lot of pressure to bring back the old PPL/FI who may instruct for remuneration; typically, the experienced hand who can give a day or two per week as he/she has another income.
Which would mean that, with fewer opportunities for 'hours builders' as FIs, the airlines might have to start taining their own pilots again. About time too!
I can think of no other industry which relies upon using apprentices as teachers.....