The PHL capacity improvement plan proposed about 5 years back has gone nowhere, and likely will never go anywhere. It would have been a 15 year phased project to effectively replace all the terminals with something resembling Atlanta's layout, with repositioned runways, etc. Unsurprisingly, I can't find a trace of that online now.
The new airport CEO was recently interviewed. Supposedly he wants to dramatically improve the experience by 2026, but it would be impossible to do any new construction by then. As for a master plan, there is supposed to be a revised one coming out next year.