They'll each complain that the other is doing X wrong and it'd be better if the other guy used exactly what we're using.. and they'd all be afraid to do the slightest pragmatic tweak (which doesn't actually affect security much, but might actually let these systems talk to each other) for fear of being called out as insecure by the others.
I'm guessing their systems would be more secure than their egos so no one would back down to get things to actually work.
Ok - that's the cynical version..
If you can find a bunch of security experts who recognize that all security is a compromise and are able to gauge relative risks well - maybe they'll even produce something with a user interface that doesn't suck.
(alright.. so it was still a slightly cynical version)