All the speculation here is really fun, but I think we should all remember it's just speculation.
Of course its impossible to tell from a pre-press release, but Shimano seem to have eliminated any chance of back-compatibility - Cassettes, Wheels & Chainrings - for little or no incremental benefit? Same number of gears, new fd shift & brifter design doesnt seem to have required these changes?
I guess required and benefit are the two words this boils down to. Of course nothing's required to change, but if you want benefit you need to change stuff. It's anyone's guess if they made these changes to make other stuff incompatible or if they did it because they thought it worked just a little bit better and were willling to sacrifice backwards compatibility.
What I really liked about Shimano is that for a long time, IME, they just didn't care about what people were saying, they just sat down and delivered a product that worked oh so well. The only time I feel they went astray from this was mechanical 7900 where they gave in and moved the shift housing under the bar tape and most of you know what that brought us.
I for one hope they go back to where they design a complete group with a kick ass performance and then the WWs in the little companies will pick it up and add their options and we'll be happy.
Gotta remember we are a minority and they need to make the best complete group that will work best on a complete bike. How boring would it be if it all just worked out right away?
I'm really looking forward to saying "But honey, this time I really need
new wheels, the other ones just won't fit."