Though the selection for your new domain can be many things, ICANN has already revoked some names. Currently, ".xxx" is not going to be allowed. In addition, trademarked names will not be available unless ownership is proven.
ICANN is also looking into charter minimums and type of format for new gTLDs. Example, 123.123 may not be available, because this can conflict with IP addresses. Also, “a.a” might not be available because it has too few characters and may not register correctly with servers.
This will likely not have a large impact on what will be available.