I have no direct experience on DL because I either have already been upgraded or FC has already fully boarded when I am boarding (I always look at the GA's screen to verify). If I am on the list I always wait to board until the bitter end, not least to minimize the time actually sitting in the Y seat. At that point I will usually be #1 on the monitor.

There is no harm in asking if there are still open seats. Either you will luck out and get one at that time, or you will be told they go by the original order. As others have noted, the main risk is overhead space, but I don't use a rollaboard and can always find space.

It's too bad DL can't establish a standard and enforce it. After a flight took off CO used to verify that no F seat left empty if there were still elites in back, and that the GA followed the proper order in upgrading. Agents were disciplined if they did not follow correct procedures. So one could board with a reasonable confidence that you would be pulled forward if appropriate.

Of course, none of this used to be a real problem for higher tier elites. Prior to about mid-2011, by my reckoning, Plats and Diamonds could reasonably expect close to 100% upgrade rates, and almost all of those happened in advance. My rates on DL in the last six months have sucked. With travel booked through the end of March, plus rollover and MQMs from credit card spend, I'll hit Platinum again but that's it. The status through Feb 2015 will help me burn through my sizable stack of miles. DL has gradually chipped away at my loyalty ever since the NW takeover, and now has completely lost it.