Could say, a Blu-Ray diode, read both BDs and HD DVDs with the proper firmware? Excuse my lack of education on combo players.

I thought there was one already. Maybe it's just the pickup they have in common.

I don't think it is the actual diode, but two different focusing lens which are needed to read both HD DVD and Blu-Ray. Both use the same wavelength laser but the data on the discs is at different locations which requires different focusing of the laser. That is one of the reasons why a HD DVD only or Blu-Ray only player would be unable to be updated via firmware to read the other format. But I could be completely wrong I'm just guessing.