Something could replace it easily if they tried to use the open standards and decentralized system like email has. But tech companies have gone too greedy, they won't make anything that works with other tech companies. Every one of them are trying to pull users to themselves. Now we have people with account in 5 different websites to communicate with different people instead.
It is sad how far the technology has come. It'd allow so much improvements in quality of life and yet it'll all being used to extract more money, making life shittier.