I have owned a car in London for 22 years and it has never, ever occurred to me to try to or to want to drive to Oxford Street.
Are you also proposing to get rid of the congestion charge and ULEZ as well as magic up non-existent parking spaces and not charge for them?
I am not au fait with disability provision but prepared to be educated in that regard. Other than that, I think your proposal, even if possible, would make Oxford Street worse not better. I think a well-done pedestrianisation scheme could make a huge difference though. It is not very relaxing to walk down at the moment, too crowded. I might be tempted to go there more often if I could stroll a bit more and grab a coffee and watch the world go by.
I would personally be extremely sad about anything that encouraged more cars onto London roads as would I imagine anyone who values clean air. e.g. there are estimated to be 600,000 asthmatics in London.