So, I'm sticking with my two dies speculation
I am pretty convinced by now — after GlobalFoundries' CTO Gary Patton stated that they have aligned certain 7LP process features with TSMC's process, and that AMD needs more capacity than GlobalFoundries can offer — that AMD has a dual-source strategy in place to mitigate the immense risk they have taken on by betting so much of their roadmap on the 7nm process leap, as well as ensuring that they have the capacity to meet their targets on market share.
However, dual-sourcing means producing mask sets at both GlobalFoundries and TSMC which is costly, time-consuming and labour-intensive. To keep risk in check, I think they will be careful to not overextend.
For these reasons, I doubt there will be a 2-CCX die. The safe route for the 7nm transition is to stick to the current MCM formula, i.e. a single 3-CCX die across Ryzen, ThreadRipper and EPYC product lines.
Also note that the 12nm Ryzen 2000 series will probably live concurrently with the 7nm 3000 series for quite some time. Its 2-CCX "Zeppelin" die will be cheaper to produce, until 7nm yield and capacity fully supplants 12nm.
So, I suspect the plan is to produce the 3-CCX "Starship" die at GlobalFoundries, with TSMC as a source for additional volume beyond GlobalFoundries' capacity, as well as serving as a backup source, if GlobalFoundries' 7LP process should falter.
An interesting question is whether AMD will also dual-source the APU. It can be argued that it makes as much, if not more, sense from a perspective of volume. That said, I would not be completely surprised, considering limited 7nm volume and risk factors, as well as hints on leaked roadmaps (see below), if the next generation APU turns out to be just a refinement of Raven Ridge on 12nm.