Personally as much as I’d love to have it, I am extremely doubtful that it will happen, at least this century. Maybe far far in the future, at least after 2150 (that is if there isn’t some new mode of transport by then), but I don’t think that anything beyond SRL East will actually be constructed in my lifetime.
It’s already quietly been shelved. The airport link was the first and most visible segment of the SRL and that part has already been officially shelved. They’re already winding down work on it.
There hasn’t been any official announcement that the SRL has been shelved but given the state of the budget and the shelved airport link it’s pretty obvious that the SRL is dead.