I think 3 years is probably about right. I don't think their modus operandi is quite a classic Microsoft style Embrace/Extend/Extinguish, probably just Embrace/Extinguish, the Extend isn't really necessary. The point is to leverage an open protocol to build a walled garden; embrace early on so your early adopters have content to interact with from the rest of the community, overcoming network effects of the fediverse having more content than them, and then extinguish once they have critical mass to pull the ladder up and leverage network effects against the fediverse. We've seen this happen before with Facebook Chat and XMPP; it took 5 years with XMPP (embrace Feb 2010, extinguish April 2015). Network effects might be slightly greater with chat than with fediverse content, so discounting below 5 years is probably sensible (although it depends on how well fediverse does, and their success of cross-promoting it from Instagram and Facebook to get critical mass).