I think Intel Foundry could also be the foundry's foundry by providing N-2 (Intel 14, 7, and 3nm) process technologies to other foundries such as UMC, GF, Tower, and even Samsung if they get out of the leading-edge process business.
I remember back in 2004 IBM, Samsung, and GF joined forces and did the Common Platform Alliance to better compete with TSMC. The goal was to develop a platform for compatible processes to share an ecosystem and allow customers to design to one PDK and split manufacturing between the foundries. This was back in the 28nm days. Unfortunately, IBM was in charge and it did not work. This is one reason why TSMC owned 28nm.
IBM's 28nm HKMG version used the gate-first implementation while Intel and TSMC used gate-last. IBM's version did not yield and the alliance failed. IBM was not known for HVM processes and they still are not even today. IBM later paid GF to take the IBM semiconductor fabs off their balance sheet and the rest is history.
Intel could easily create a common platform for other foundries providing the fabs, PDKs, and ecosystem. The margins may not be big but it could fill Intel fabs which, in my opinion, is the root cause of Intel's problem. They have to fill the fabs.