The Red crank has an interesting weight-to-price ratio. Idealogical aspects asice¹, what would my chances for getting it to work in a DA drivetrain be? SRAM says it only works with the Red 2012 FD.

¹ I'd strip the paint anyway

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Bikes: Raceur, Beateur

The only real differences between one 10 speed chainring and another are in the lifting pins and tooth shaping. Given that chainrings are normally exchangeable (DA, Stronglight, Tune, Extralite...) I expect the SRAM chainrings will work just fine in a DA system.

Does that mean the SRAM chainring spacing is consistent with DA?

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Bikes: Raceur, Beateur

In almost all cases, 10-speed chainrings match any other 10-speed system. Hence, SRAM cassettes and chains are compatible with Shimano cassettes and chain that run 10-speed. Same with the chainrings. You'll run them fine

I run all sorts of Chains, KMC, Shimano on my Red full groupset with DuraAce cassette and Rotor Qrings.

All works fine.

if I recall, the new red rings are spaced further apart on the cranks - something like 1.1mm. I don't know if that's a spacing difference with the rings, or the crank.

I'd guess that the DA front derailleur would probably work fine, but it also wouldn't surprise me to see more chain rub than normal with the setup. If the spacing is in the rings, you could swap the relatively heavy rings out for something else.