I think there is a lot of people who prefer to re-use as much as possible of what they currently have before they have to throw everything away.. Our current Eth and Wifi shields, to mention two, work with the Due as they are able to detect and adapt to the whatever voltage the main board is operating at.
But in reality how much shield re-use will there really be? (I'm guessing not much)
There are many things that will prevent existing shields from being used.
- 5v outputs driving the Arduino input pins
- depending on certain alternate being functions on certain pins
- Current demand on Arduino output pins
being some of the biggest issues.
Normally when electrically damaging incompatibilities exist,
connectors/pinouts/headers are changed to ensure that such devices
are never allowed to be connected to each other.
Just my opinion but preserving the existing header layout is creating a much
bigger problem than it is trying to solve.
It now makes the selection of which shield to buy/use no longer simple as there
will be shields that will plug into the DUE that can damage it.
Not good for newbies and less technical users who will tend to have the view
that "if it fits" it must be ok.
Making the board 5v tolerant would have made the it way too expensive.
Ah. Finally, A definite answer on the 5v tolerant question.
Too expensive for whom? The naive user that blows up his DUE or schools that have
students blowing up DUE boards when trying to use an incompatible shield may not
think the money saved for this lack of protection on DUE was worth it.
There are other 32 bit MCUs out there that are 5v tolerant that would not
have incurred the additional cost that might have been better suited
for this type of environment.