- .aero: if IATA airport codes were all registered domains here, it might be useful, but they aren't, so it isn't.
- .asia: asia is definitely a country </sarcasm>
- .biz: sufficiently stupid that SpamAssassin has a rule for it
- .cat: meow? seriously, I've only seen this used for vanity joke domains
- .coop: there isn't a .llc, why is this any different?
- .info: happy fun SEO land
- .jobs: pity they won't take my registration for Blow, Inc.
- .mobi: as noted
- .museum: 1138 registered domains in 10 years is a sign of true irrelevance
- .name: personal names are hardly unique identifiers
- .pro: stupid hierarchy makes this one even more useless than you'd think
- .tel: as noted
- .travel: because .aero just wasn't enough
- .xxx: as noted
Perhaps I'm just not seeing the possibilities, but I suspect that there's no future for any of the gTLDs beyond com/net/org, and possibly a few of the up-and-coming IDN gTLDs. The future of domain names is really in better unique names, not a more complex hierarchy.