Based on our experience, this would be possible (we're going to implement Hol. in a 15p department of a 2500 people org.) , nevertheless I would recommend if possible to implement in a piece of the organization including at least 2 or more conventional hierarchical layers to get the benefits from Holacracy.
Here is an example with a pilot of 50 people in a 70 000 people group
Of course you will not get the full benefits of Holacracy when applying in only a part of the whole org. but almost 60% based on what Dannon (another client) estimates.
Hope this helps