Protease inhibitors are targeted at a specific enzyme, C3L in this case. Pfizer actually started working on a C3L protease inhibitor back in 2003 to treat SARS, but SARS went away and they shelved the project. There are other studies into C3L inhibitors against coronaviruses. The 2 C3L PI drugs Pfizer is working on (1 IV and 1 pill) could potentially work against all coronaviruses.
Are you saying we might finally have a cure for the common cold after all these drippy red-eyed thousands of years?