Actually it will make it harder not easier. At the moment many people use the station car park and then hop on a shuttle bus to the terminal but this is what the airport say.
Although a multi storey car park is provided for Network Rail users, it is not envisaged that this will be used by users of the MPT due to having to buy a ticket and walk through the Network Rail station to access the MPT.
So you can only access the station if you buy a rail ticket but maybe they will sell tickets to access the MPT for anyone not arriving by train?
Sometime ago there was a plan mooted to build a multistory next to the MPT at Parkway to be used as a long term airport car park but at the moment that plan seems to have been dropped as only 12 parking spaces will be provided for staff.