There are a few very small incompatible changes - I really doubt most people will ever run into them.
Putting Windows [3.11] on top of DOS is like putting whipped cream on a road apple [horse poop].
It's there as a sop to former Ada programmers.
Adapting old programs to fit new machines usually means adapting new machines to behave like old ones.
Except for its backward compatibility with existing Wii software and accessories, we have so far failed to make propositions worthy of Wii U's position as a successor to the Wii system.
From day one our next generation system will run all our exsisting software - so that gives us a head start.
There is no schedule. We are all volunteers, so we get it done when we get it done. Perl 5 still works fine, and we plan to take the right amount of time on Perl 6.
Why should someone have to retrain themselves to use a new application that does the same basic thing as the old application, just because something as trivial as the operating system changed out from under them?
Well, the first thing to say is that we've worked hard to maintain compatibility, so that any program written with an earlier version of Mathematica can run without change in 3.0, and any notebook can be converted.
Crappy old OSes have value in the basically negative sense that changing to new ones makes us wish we'd never been born.
