Will the new iphone 5 have pure digital output via lighting connector?

I'm an audiophile who wants to use external DAC for the upcoming iphone 5. Will the iphone 5 have the compatibility to do so?

Nope

If you want video out, don't get the iphone 5. Only older iphones currently support video out through the cable.
Newer apps will run smoother on the iphone 5. Depends on your needs and wants.

DAC requires an authentication chip and apple approval of the device, that's why there's so few on the market at this point. I don't see these requirements changing for the Lightning connection.