It is believed all the engine manufacturers already involved in F1, and potentially some others interested in joining beyond 2020, want the next units to be 1000hp, louder, simpler and cheaper.
Rumor has it that in order for IndyCar to be somewhat relevant to hybrid passenger cars IndyCar will also have to implement a single KERS so the talk is why not have a universal open wheel engine and have both series run a 1.6 liter V6 with two turbos and a single KERS.
Why would IndyCar do this? To get F1 teams and manufacturers to run a car in the Indy 500.
The issue for IndyCar will be the sustained speed required at Indy and whether a 1.6 liter engine can generate enough HP and last 500-miles.