The problem with crediting CO miles to DL is that you will lose any chance of CO upgrades. EWR is so far from SEA.
I had never heard of the DL-AS reciprocol upgrades. Can someone post a link?
Basically this is a program yet to be implemented. Its supposed to be similar to the one AS & NW currently have... (partner elites ug'd after all of primary carrier's elite's ug'd)...
There was a thread in the AS forum... but this has not been implemented yet (only announced) so almost exciting
As far as SEA-EWR... AS does fly this route too, and although its difficult to UG on that route, I've done it before... so it's possible