A Major Change
This sure is a major change for the people that have to support the new devices. It's fine if you know in advance that you need to support Macs, and you spend time upfront planning and putting systems in place to manage them. If you try to add Macs to an existing Windows environment though, don't expect it to be a smooth integration.
The equivalent in the building industry would be to have an architect design a skyrise, have a building company spend two years constructing it, and then once it's up deciding that it actually needs to be four stories higher now.