I'm not confining this discussion to 1/10 sedans, or even on-road.
I'd like to see 1/12 go to at least 10 minute mains, even 15.
There is a local guy here who races in a modified 17 turn touring class that we have, he often uses the same batterypack for 2 heats, not charging between. His packs are old 2400 mAh NiCd cells and 3000 mAh NiMh. And he wins a race now and then.
So how about starting with 8 minute mains for 19 turn motors? Letting modified 8 minute races wait a bit.
It has been repeatedly proven that you can dump any 6 cell battery with any motor less than 10 turns in 4 minutes if you time it "correctly". No problem.
But you can also make almost any motor last at least 10 minutes at 98% of current racing speeds using 3300 batteries.
Length of races could be a problem, but if you limit drivers to 2 classes or fewer in the same race you can easily reduce that problem, even elimite it.
If you have extra 3 minutes you could make up for the first corner carnage.
After racing eight minutes for couple of races, I bet you can't understand how you could race in the much too short five minute races.