I'll go with the concensus here.
I think that the consulting engineer wants to re-think that little idea.
Lets look at it this way Kiwi, most switch-board enclosures are to a degree IP rated, most are at the very least IP 23.
What does this guy want?, all switchboards in installations to be IP 55, 65 or even the submersible rating of IP 68.
Fact is, a sprinkler head will only be activated if there is a need for it to be.
One other thing that springs to mind Kiwi, has this guy actually thought about how you get rid of the heat out of such an enclosure, all switchboards emit heat to some degree.
Also, should the IP rating apply to the whole switch-board enclosure?.
Why not just the top and sides of it?, and a sealing gland in the door, which I am sure most Vynco branded boards already have.
Considering that Fire Service response times these days are pretty good, the chances of actually soaking a switch-board unit, before the sprinklers are shut down and the fire attack happens, are pretty remote.
Just my $0.02 worth.