I wasn't referring to King-Byng in terms of coalitions being good (they can be, this one would not), but the fact that a GG overruling a PM will always be deeply controversial. And King-Byng happened at a time when England didn't interfere with Canada's government out of lack of interest rather than Canada's being independent. The controversy that incident created led directly to the Statute of Westminster, which significantly altered how Canada, Australia, New Zealand and others were governed.
Also, you are wrong in calling Meighan's government a coalition - it wasn't. At least no more so than the Liberals and NDP cooperating on an issue would have been today. The comparable scenario would have been if Johnston refused Harper's request for an election and asked Ignatieff if he could form a minority government, irrespective of the NDP or Bloc's involvement.
The only other example I am aware of of a GG using reserve powers in this fashion was in
Austrailia in 1975, and led directly to three constitutional changes. GG's don't interfere without very good reason.