Thameslink already has two quite separate services, the metro (via the
Sutton Loop), and the Bedford to Brighton. It would make perfect sense
for
LOROL to control the metro service, but not the long distance.
Except late at night when the trains run all stops Bedford - St P, and
during the peaks when the service patterns get complicated. They also
share stock and depots and drivers. It would take a major
reorganisation to try to run the metro service as a separate
operation.

Not so.
Since Govia days, their has been designated stock, and while there are
exceptions, diagrams, trains and drivers could very easily be separated. By
the time TL2000 is complete, there will be three, maybe four depots
involved, so if sharing was too painful, one could be separated out.

It really wouldn't be difficult, and would allow Boris' Lorol Map to look
much better, while service levels (and possibly times) needn't change
immediately at all; next would be the South London, followed by the Moorgate
services, that neither WAGN nor CursedGroup have ever cared about. In fact
there's really no reason why London shouldn't have its own network of
all-stations-metro trains. Is there? And I'm sure the TOCS would be happy
not be pressured to match LOROL's standards of station staffing ...

Yes, it'll take years; it may even take a non-tory mayor or two.