Chris Pratt, I think, is worthy of being the new front man of the MCU, at least for a little while. Guardians are extremely popular and adding Thor in makes them that much more of a must see movie.
I actually think they might wait 5+ years until the next Avengers. In the meantime they can use Guardians and Black Panther as the top box-office event movie of the year. Both series are extremely popular.