This is doable too, if we have a clear consensus on what would be
a reasonable default on TYPE_MACHINE. Personally I prefer the
default on TYPE_MACHINE to be "none".
Yes, please, no magic default hardware for all machines. That will only
cause confusion and problems in the future. People who add new boards
will keep forgetting to set a value in their new boards and then you
later wonder whether that was on purpose or by accident ==> If there is
no default display set, this should simply mean "no display".