Highways England have made their response to the new stadium proposal (as amended to be just the football stadium complex on the north side of the A419). In summary they require that conditions are attached to any planning permission to say that specified road improvements both to the A419 and the M5 junction are to be completed FIRST.
The required mitigation measures include the dualling of the A419 carriageway between M5 J13 and the Chipmans Platt Roundabout and changes to the white lining and signing at M5 J13, to allow greater capacity to be achieved from this junction. This allows for both lanes of the northbound and southbound off slips to be used to travel east, exiting via the A419 towards Stonehouse.
You can read their full response here:-