I suspect that you will see minimal investment in T1 as each £ spent on it is a £ that can’t be spent finishing the T2 transformation programme - which does need to be the absolute priority from an infrastructure perspective. Don’t forget T1 was meant to have closed permanently by now so they will be reluctant to throw money at an asset they are going to demolish.
Adding a dedicated domestic facility would also likely make the situation worse not better when they’re struggling to staff current operations.