Various ideas have been put forward for experienced PPL holders to instruct for remuneration at PPL level.
But none are likely to see the light of day for many years yet. If at all.
You do not need a CPL to instruct at PPL level unless you want to be paid for it. Even if you didn't want to be paid, you would still need to pass ALL the JAR-FCL CPL exams....as well as being accepted for FI training.