I would not be too excited about reaching new milestones in fuel efficiency because of the motorsport battlefield.
For road cars, everything rotates around real world loads of the engine, i.e. an extremely high percentage of part load time.
In formula racing, part load is a very small percentage of the duty cycle. Gains in part load are necessarily much smaller for a racing car then they are for road cars (where they are essential).
Future full load gains are small for sure, and pretty expensive.
I think we'll see a battle about who has the best set of preselected mappings to have the best usage for the ES over one lap, which will change from circuit to circuit. It'll be a battle of simulators, and I wonder how the constructors will help the customer teams with this data, especially in Renaults case, as I think they are depending much on simulator data from the teams which have one...
OT, if car manufacturers want to showcase their "green" competence and be ready to spend the needed, considerable amount of money, I do not think traditional motorsports, and especially not F1, would be the way to go. They rather should set up a new formula, with windmills and photovoltaic panels, batteries and electricity to hydrogen conversion and what not, and then compete on track with the available stored energy. Would be fun to watch, a complete energy production and consumption chain would be in competition, and maybe it would be in for real new leaps forward in green technology.
Apart that, I'm also sceptical that more then 4-5 manufacturers may have interest in competing all in the same formula, but it's OT anyway, sorry.