Personally, and I'm just spit balling, if PowerPlay is the PvP mode of choice (and open only?), any PowerPlay related deaths should be entirely, or mostly covered by the power you work for.
Unrelated deaths, such as crashes or docking snafu's aren't covered.
PvP then gets a playability boost, and the factions "economy" can also be based on how many rebuys they're forking out for per system, and overall.
You wanna attack a specific system? Then simply cost the faction a shed load of credits by killing CMDRs and NPC's.
Wanna support it? Bring in goods and boost its economy via any number of methods, trade, mining, etc.
PowerPlay conflict zones can have an overall resource per zone, and each time an ship is lost, it costs that faction some resources. No more resources means no more reinforcements, which means the other team wins. Or something along those lines...
I think I just fixed PowerPlay by accident...
Sounds reasonable.