New Website - Question

I have a client who is optimizing his website for several years for specific city and he has good positions for his main keywords. But now he wants to expand his business in another bigger city.

What is your opinion?

A: We make subdomain for the new website;
B: We move the old website to subdomain and we change SEO in the main domain for the new one.

Make a subdomain for the new website. It will help to organise the content better.