currently nobody apart from Mercedes likes the system in place. I have two solutions that i think would help solve the issue in a fair manor without upsetting the fans 1 could be in place as just a rule change while the other might require a change of engine regulations.
1. each engine must do 5 races without swapping out for another motor. like the gear box rule.
teams could use any motor they like in practice sessions on Friday so that number of laps are not reduced. p3 must use race engine. if the team has to use a new unit before race five they must take a 5 place grid drop per component. keeping the engine in the car until the end of the original 5 races. At the end of the 5 races it would be retired from racing keeping teams on the same plane. this would stop teams piling up grid pens by swapping them out before failure all for them to be used at the end of the season and fail. this is better than the current system which basically means a bad start ruins your whole year. while you would still be punished for poor reliability it would be early and steady unlike the current system that means once you have used your engines you get pens every new part afterwards destroying the end of season for some teams.
option 2 would be to have 1 engine per season. free use of different units for Friday practice but race unit from p3 on wards teams would get a grid pen equal to the amount of cars on grid (ensuring they start last apart from cars that qualified behind them and also used a new unit) for any new unit used but the whole unit must be changed upgrades would be seen as a new unit and would be punished just the same as a failed unit