According to recent details that appeared in the British media recently, it looks like German automaker Porsche plans to return in F1. 
Matthias Mueller, Porsche’s new chairman said that either Porsche or Audi is expected to compete in the LMP1 prototype sports car racing, and whichever brand will not go into LMP1 will head to Formula 1.
Matthias Mueller does not want Audi and Porsche to compete in the LMP1 against eachother but before taking a decision "we have to discuss whether it makes better sense for one of
the brands to go into LMP1, and the other brand into Formula 1. So
we will have a round-table to discuss the pros and cons," he said.
As Volkswagen has flirted with the idea of becoming an engine supplier for Formula 1 in 2012 or 2013, then Porsche’s comeback to F1 seems like a logical step.
Porsche has stopped racing in F1 since 1991, back when they are an engine supplier as well for the Footwork team.

Source: Autocar