I'm able to http -h 184.108.40.206 and get a valid response, but using http -h 2607:f8b0:400a:801::100e produces the following for me:
http -h 220.127.116.11
http -h 2607:f8b0:400a:801::100e
http: error: LocationParseError: Failed to parse: Failed to parse: 2607:f8b0:400a:801::100e
It would seem that httpie doesn't support direct IPv6 address input as http -h ipv6.google.com works fine.
http -h ipv6.google.com
It's a bug in requests/urllib3: kennethreitz/requests#1426
Keeping this open for reference.