http://www.mountwhitneyforum.com/ubbthreads.php?ubb=showflat&Number=105360#Post105360 provides an update on the road conditions I saw up there...
Based on what I saw at Onion Valley a few days ago, the major melt hasn't hit the 9k'+ level yet...so, I don't think HM Rd will be open for Memorial Day (I hope I'm wrong)...there was still at least 3' of snow on the ground at that level...
As Doug states, there's way too much potential for anyone towing a trailer (or in a longer vehicle) to get in trouble and not be able to head back down if the route all the way to to the trailhead isn't clear...so I doubt they'd open to a lower locked gate like they sometimes do on WP Rd...
I do love being up there by myself, so I'll keep riding up there and post reports on what I see...