Throughout our history in the federal government, we've merged different departments easily enough. It's not the first time and it won't be the last, so to do it isn't a complication.
I will say, though, that in departments it could be perceived as a win-lose, so my comment has always been that unless the Prime Minister orders it to be done, it won't be done. Staff in PSPC, I'm sure, would much rather go to air shows in Le Bourget or Farnborough than worry about buying furniture for the Crown.
People enjoy this, and I understand that. One minister may seem to be losing if they're not part of the big billion-dollar announcement. I understand that, so I don't think it's going to happen from the bottom up. I think the Prime Minister has to order it if it's ever going to be done.