On the Piccadilly approach from the east theres a reserved bit of land near Ashburys that would serve as an off ramp to street level. Approaching Victoria from the west no routes ever been suggested by officials though a direct Wigan-Marple service was an aspiration in the 90's supported by the rail industry, if they wanted to street run I would place a high chance on a street connection near Salford Crescent.
Of course they dont have to physically connect, a doubled frequency on the Atherton line with a service terminating in new western bays at Victoria for instance. The current limitation is the signalling headways on the Atherton line limiting frequency and the cost of improving them. So for example a tram train scheme could resignal the line as light rail, electrify at 750v, double the service frequency, add more stops (with the trains still benefiting from increased acceleration of electrification) then share the existing infrastructure from the end of the Atherton line to Victoria switching to 25kv and vice versa at the other end for the short stretch to Wigan. It would be cheaper to install and maintain and operate than a comparable heavy rail scheme making improvements currently considered unprofitable, practicable.