Lead free 100 RON fuel won't be hard to make.
Mobil's 8000 premium unleaded product is already within a bee's whatsit at a claimed 98 RON. That's done without even using the different chemistry of AVGAS.
As for valve lubrication and valve seat recession- aviation engines already have inserts for seats. Not hard for valves and seats to be made compatible with lead free fuel.
In the meantime phosphorus based lubrication could be used, as with lead replacement petrol (today's lead free super).
In short making it work won't be a problem, but expect possible reduced TBOs for a few years. On the other hand say goodbye to lead fouled plugs.
Engines requiring 130 RON fuel (green stuff) such as turbocharged models will probably have to carry on using lead however.