Last year I saw a PA28 with a Thielert Diesel engine.
It was fitted with a VP propeller and a turbo charger. The engine controls was:
1 lever (electronics do the injection timing and pitch control)
1 starter key (like any car)
1 fuel selector (the standard PS28).
The engine has been approved by JAA for PA28 and C172 - so we are getting there. Furthermore the fuel consumption is reduced by apprx. 40% and it runs on dieselfuel or JET-A1.