That will no longer be possible. Also, it will not possible to just assume that the TLD is the new domain name, with every middle-sized company snatching up their brand name as TLD.
So when that expectation is no longer there, there will be no problems at all. Some of these TLDs will work similar to the existing generic TLDs, with the possibility for third parties to buy regular domains. Others will operate more like private tropical islands, used as some kind of status symbol.
The whole thing has one likely positive consequence, though. It might weaken the idea that you could somehow own a name or word. Some arbitrary slightly deep-pocketed entity grabs a name that most legitimately interested people cannot afford. That happens often enough, and nobody gives much about that name plaque any longer. Plus, old-fashioned brand operators will have a tough time buying up all "their" domains under the newly formed TLDs until they eventually give up and realize they cannot control "their" name in every conceivable abstract namespace. Everyone wins.