For instance, Google could go from google.com to just google. It won’t be cheap though, at an estimated 100,000$+, and only big corporations would be able to afford the price tag.
This could lead to cheaper (or free) second level domain names. Currently, .com domains cost around $10, of which around 6.42$ goes to Verisign, the authoritative registry of the .com tld. This completely artificial pricing is what has made alternative domains like .tk so popular that it contributes 10% of the GDP of the Tokelau island.
With the freeing up of top level domains, Google (or someone else) could buy a generic tld (.go, .web, .site) and make second level domain names completely free. Not only would this provide a viable free alternative to .com, but also drive down the arbitrary pricing imposed by Verisign.