portability

Cant you change from shimano to other brand derailleurs? Isnt there a standard derailleur hanger that fits all derailleurs?
I saw some bikes with removable derailleur hangers.
Disk brakes fittings seem to be standardized.

yes certain things work, you can have a mix of components but not change the complete group from one to the other.

1. why would you want to? its not as if for any given race there is an advantage of one system over the other.

2. to some degree you can, pretty much everything SRAM is interchangeable with shimano and so is Microshift. Campy shifters can be made to work with pretty much all shimano drivetrains.

I'm not sure I get what you are talking about. You can already swap between groupsets with the same frame if you so desire. It has been this way quite some time.

Or are you talking about being able to mix and match?
Are you talking about the growth in the number of different BB "standards"?
Are you talking about the lack of interoperability between levers and derailleurs of different brands, or levers and brakes?
The fact there are two different spline patterns on freehub bodies for the different manufacturers' cassettes?

This last point could easily be improved. Campagnolo already offer a HG (Shimano/SRAM) compatible cassette carrier for their wheels and hubs. Unfortunately Shimano have never seen the need to reciprocate.