As for short haul routes to some extent it depends on how independent and innovative the new short haul subsidiary is allowed to be. There may be even be scope for limited feeders for the long haul operation.
Although I agree domestics may not be the initial focus, pre-Covid BA was carrying about a few hundred thousand a year between London Gatwick and Edinburgh. There is probably a fairly decent point to point market
for some domestic services. Likewise Jersey may warrant a seasonal service from Gatwick. Amsterdam and Rome were served from Gatwick, but catering more for point to point leisure travellers. The cheaper cost of Gatwick
allowed BA holidays to offer some good value city breaks. To some extent it may depend on how demand for certain destinations recovers at Heathrow and pressure on BA slots at that airport. Increasing charges at Heathrow and
the third runway seeming further away than ever ,will also have a bearing on BAs plans for Gatwick both long-haul and short-haul.