Nobody's trying to reconfigure Mississauga's entire transit system.
I was referring to the post that I quoted, which suggested just that.
If a real regional rail system is built with a link to MCC there's nothing stopping LRT along Hurontario, or whatever else could be done to improve local transit in Mississauga. If local transit improvement is the goal then spending billions to extend the Bloor Danforth line isn't the answer.
Yes, simply diverting the Milton line to serve MCC is cheap in comparison to a subway (not that I suggest the B-D line be extended to MCC in the first place), but having two rapid transit lines along Hurontario is redundant and upgrading the Milton line so that it can handle all the extra trains would probably cost billions just a like subway.
If the MCC diversion becomes a spur for the existing Milton line, the service would be very poor because there is very little capacity on the rest of line, even considering the third track that is going to be laid down. The MCC, Erindale, and Cooksville stations would see 20-30 minute at best during rush hour and maximum 2 hour frequency during off-peak times. So basically, the three busiest stations on the Milton line would have half the service as the other stations on the line. This does not make sense to me at all.
A diversion to MCC can work if the Cooksville and Erindale stations are taken out of service, but this is not an ideal solution either, because Cooksville is one the few GO stations that is in decent location and, as I said, it is, along with Erindale, the busiest on the Milton line and second busiest in all Mississauga (actually busier than Port Credit station).
And of course, an MCC diversion doesn't help anyone in Mississauga get there easier. You'd be spending billions just so MCC can have better (yet still very infrequent) connection downtown Toronto and ONLY downtown Toronto, and at the same time make it worse for other parts of Mississauga.