Lighttpd

RFC2616¶

14.23 Host
   Host = "Host" ":" host [ ":" port ] ;

3.2.1 General Syntax
   RFC 2396 [42] (which replaces RFCs
   1738 [4] and RFC 1808 [11]). This specification adopts the
   definitions of "URI-reference", "absoluteURI", "relativeURI", "port",
   "host","abs_path", "rel_path", and "authority" from that
   specification.

RFC2396¶

3.2.2. Server-based Naming Authority

      host          = hostname | IPv4address
      hostname      = *( domainlabel "." ) toplabel [ "." ]
      domainlabel   = alphanum | alphanum *( alphanum | "-" ) alphanum
      toplabel      = alpha | alpha *( alphanum | "-" ) alphanum

So toplabel is alpha.
ICANN´s mentioned "ideas" from #2143 are just a "Draft".

Hi,

First : Our company uses Numeric only TLD's internal. Lighttpd is the only soft to fail with that.
Also, ICANN does not say TLD 'MUST' be alpha, but "MAY NOT" be full numerical.

also : http://www.ietf.org/mail-archive/web/dnsop/current/msg08941.html

ietf is using pseudo-TLD's to test numericals tld.