I have a question, so DTG has the TfL license, right? If so then I suppose that would be a great opportunity to create the Elizabeth line (I'm not suggesting, just saying) The thing I see which appears to be an issue is: can DTG update the GWML even without a license?
Dovetail has a license with TfL - at the very minimum for Over/Underground - yes. It could extend to include the TfL Rail/Elizabeth Line license. Dovetail could upgrade London-Reading without a license, but it would require them to stick with the HSTs and 166s for GWR, if (as speculated) the GWR license is gone.
