Can't see that working tbh. Shutting Oxford Rd would mean the 2tph CLC services would have to terminate at Piccadilly instead, making P13/P14 busier. Additionally - given guard/driver swaps for Northern services happen at Occy Rd would need to happen at Pic instead, again making P13/14 busier especially if a guard/driver is late and a train gets stuck at Pic (as what happens at Oxford Rd currently). Deansgate is also really popular for commuters - particularly thanks to easy metrolink connections.
I do wish the three stations got a propper rethink and the section needs investment such as desperately needed additional capacity. I just doubt closing the two stations would help as such.
Personally - I don't see why its too much to ask for Manchester to get four tracks on the entirety of the Castlefield corridor.
If we were London - the section would be given an additional six tracks by now and Piccadilly would be 30 platforms