There are currently no upgrades to DL Comfort+ and AS Elites are not eligible for free access to those seats. Starting May 16th, domestic Comfort+ is considered a separate booking class and there will be an upgrade list for it. Whether AS Elites will be eligible for the Comfort+ upgrade list starting May 16th is an open question. I'm guessing not as it would likely be something DL/AS would have to negotiate and they aren't really in the negotiating mood these days.