The latest "new TLD" thing was a money-making scheme for domain registrars. Nobody goes to those domains. Even the previous round of TLDs (".museum", ".aero") are not used much; ".aero" has entries for all the major airport codes, but they're redirects.
Amusingly, even if you have your very own TLD, it doesn't help you. Most browsers send single-word lookups to a search engine before they send them to DNS. Try "ca" in a browser. There is a web site at "ca". But to get there, you'll have to use "ca.", to force a DNS lookup from the root. Nobody knows to do that unless they're into how DNS works. There are some low-level bugs embedded in very common C libraries which cause problems with single-word domains, and they probably won't be fixed.
As for the original poster's advice, the price of the domain you want in .com is probably more than YCombinator's initial funding. With all of today's domain hoarding, the ".com" domain usually comes later. Facebook started as "thefacebook.com".
$ nslookup ai
Server: 127.0.1.1
Address: 127.0.1.1#53
Non-authoritative answer:
Name: ai
Address: 209.59.119.34
Rechecking using Google's DNS server:
$ nslookup
> server 8.8.8.8
Default server: 8.8.8.8
Address: 8.8.8.8#53
> ai
Server: 8.8.8.8
Address: 8.8.8.8#53
Non-authoritative answer:
Name: ai
Address: 209.59.119.34
It's pingable:
$ ping ai
PING ai (209.59.119.34) 56(84) bytes of data.
64 bytes from offshore.ai (209.59.119.34): icmp_seq=1 ttl=46 time=133 ms
64 bytes from offshore.ai (209.59.119.34): icmp_seq=2 ttl=46 time=132 ms
64 bytes from offshore.ai (209.59.119.34): icmp_seq=3 ttl=46 time=132 ms
...
And it speaks HTTP:
$ wget ai
--2015-08-09 14:26:26-- http://ai/
Resolving ai (ai)... 209.59.119.34
Connecting to ai (ai)|209.59.119.34|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 1257 (1.2K) [text/html]
Saving to: ‘index.html’
100%[======================================>] 1,257 --.-K/s in 0.001s
2015-08-09 14:26:26 (842 KB/s) - ‘index.html’ saved [1257/1257]
It doesn't respond to HTTPS, though. So we don't get to see a cert issued for a TLD.
A base level TLD site is rare; most TLDs don't have one. But it's supported in DNS.
Well, at least prg.aero is actual website and not redirect (which may have something to do with the fact that ownership structure of the airport had changed around the time .aero was introduced).
Amusingly, even if you have your very own TLD, it doesn't help you. Most browsers send single-word lookups to a search engine before they send them to DNS. Try "ca" in a browser. There is a web site at "ca". But to get there, you'll have to use "ca.", to force a DNS lookup from the root. Nobody knows to do that unless they're into how DNS works. There are some low-level bugs embedded in very common C libraries which cause problems with single-word domains, and they probably won't be fixed.
As for the original poster's advice, the price of the domain you want in .com is probably more than YCombinator's initial funding. With all of today's domain hoarding, the ".com" domain usually comes later. Facebook started as "thefacebook.com".