Now not only has TSMC or Samsung shrank the gap to less then a year or so, they now both enjoy the same economy of scale provided by the mobile phone market. 1.7 Billion Smartphones Vs 250M PC. While many of the smartphones aren't using cutting edge tech, the same goes to PC market as well.
Unless there is any change of pace from Intel, TSMC will likely have the same level of tech as Intel in 2019, and a scale that Intel wont match assuming Apple dont change course and continue to Fab with TSMC.
They will need to sell more chips, more transistor, keep the Fab fully utilize, with the ~200M Modem from Apple next year that is going to help tremendously, but given Apple switch supplier from time to time their move into GPU in 2 - 3 years time seems like a backup plan incase anything goes south.