Charlie,

The coil has its own "driver circuit" within the MS controller.

I don't think there is a way to wire it up
otherwise, on the megasquirt. Only the dizzy gets "switched",
unless you're using crank sensors.
And it doesn't really require a relay, except for convenience
<i.e. one COULD use the ignition switch B+>.

If the MS is off, the coil sees no current, correct?

And there is NO need for a switched relay "port" to intermediate this connection,
it just gets accessed using a "relay board" as an interface.

Am I missing a subtlety in
your post? I wholeheartedly agree; keeping it simple is good.

--frankb