Back in March, FOM, the FIA, and multiple global auto manufacturers, some involved in F1, and some not, met to lay the groundwork for the engines to be used starting in 2021. VAG attended, represented by Audi, which led to speculation of a looming partnership between Audi and Sauber. This past Monday, a followup meeting was held, with engineering firms Cosworth, Zytek, and Magneti Marelli, as well as automaker Aston Martin in attendance. Zytek and Magneti Marelli's primary interest was likely in the electronic control systems for the upcoming engines, as both companies specialize in the field of motorsport and other high-grade automotive electronics.
Cosworth and Aston Martin, however, have no known vested interest in the sport. Neither specialize in top-end electronics, but both have been linked in recent history with Formula One. Aston Martin has been alleged to be entering Formula One with its own team multiple times in the last decade, and through the end of the V-8 era in 2013, Cosworth was an engine supplier for the now-defunct Marussia team. Neither of these companies are likely entrants for 2021, however.
Aston Martin is outsourcing the design of its current production car engines to Mercedes AMG, because they simply cannot afford to design their own engines. The old 5.9 liter V-12 used in most Aston Martins for over a decade was actually just a pair of Ford Duratec 3.0 liter V-6 engines joined together longitudinally. No company that cannot afford to design and manufacture its own engines is capable of fielding a self-titled Formula One team— never mind the fact that the brand is already a sponsor of Red Bull Racing.
Cosworth itself designed an engine for the current 1.6 liter turbo V-6 era, but concerns over the company's ability to keep the engine competitive in the long run scared away potential customers, so the engine was never raced. The firm's presence at the engine meeting can be taken as evidence that Cosworth is still interested in Formula One, though it will be a challenge for them to find a willing partner team by 2021.