I am constantly amazed when I come into these forums at the amount of misinformation and "opinion as fact" gets tossed around.
I have been a member of several consortiums and multi company standards committees. I was the architect and leader of three of them. Here are some more facts from the trenches.
First, the object of a standard is not to produce the best technical standard possible. It is to provide a workable standard that can be adopted by a wide range of users. I always told my committees that the goal was to come up with the second best standard, as the group would never be able to agree on the first best one.
Second, groups looking to extend existing standards, or to add optional components MUST consider backward compatibility as the first priority. This means that any disc produced must act reasonably on any player produced. A good example is when VHS and Laserdisc added digital tracks. Each specified that the original analog tracks must be retained. Further, when stereo analog tracks were added, the weren't simply left and right. Rather, they laid down L+R on top of the older mono track and added L-R on the new track. That way, older mono machines would play the entire soundtrack in mono.
If the BD Alliance intends to keep any credibility, they will recognize this and specify that Any compliant player at any level will be able to play any compliant disc. New features may not be available, but the basic 1.0 functionality will be.
Therefore, you should be able to play any disc on a 1.0 player. You may lose features, but the basic functionality should allow the player to access all the 1.0 capabilities on the disc.
If they don't do this, they then obsolete and alienate their existing customers. I expectthese players to get better over time, with new features. I will buy new players, but I can expect to be able to move the old player too the bedroom and continue to enjoy it. It also means that manufacturers can continue to produce to the older standard and customers can expect the player to play discs.