I can't claim to be the ultimate expert on this subject, but from what I have seen, the problem appears to simply be that we don't know.
I agree with Gonk... and add, that if we take history to lesson, the connection which will pass a protected signal will change as the HD-DVD/Bluray players are produced and begin to evolve.
When SD-DVDs started, component video was considered de-rigor for up to HD resolution connections. Then Hollywood got paranoid, and us early adopting HDTV owners got screwed by SD-DVD players which only gave their best resolutions via DVI-D/HDMI connections.
Unless you've got LOTS of money to blow.... I'd wait to buy into HD-DVD/Bluray until they are at least a few versions into the format... otherwise, prepare to buy a new display to match Hollywoods paranoia.
Those who don't learn from history, are doomed to repeat it.