Back in the day, 2007 and 2008 there was live running federation between Twitter and Jaiku. I remember i was sitting in the room when Ralph and Blaine got it working, at 4am at a foo camp.
Unfortunately Jaiku was bought by google and they spent a long time with it offline only to come out as Google Buzz which didn't take off.
Many of the early twitter engineers like Blaine Cook and Alex Payne pushed hard for twitter to be more open and federated, but lost that argument and left or were pushed out. It's a business not a technology decision which makes twitter centralized.
Unfortunately Jaiku was bought by google and they spent a long time with it offline only to come out as Google Buzz which didn't take off.
Many of the early twitter engineers like Blaine Cook and Alex Payne pushed hard for twitter to be more open and federated, but lost that argument and left or were pushed out. It's a business not a technology decision which makes twitter centralized.