The experience of the ISP Free in France:

   After having had a succinct presentation of the 6rd idea, a major
   French Internet service provider (ISP), Free of the Iliad group
   (hereafter Free), did all of the following in an impressively short
   delay of only five weeks (November 7th to December 11th 2007):

   1.  obtained from its regional Internet Registry (RIR) an IPv6
       prefix, the length of which was that allocated without a
       justification and a delay to examine it, namely /32;

   2.  added 6rd support to the software of its Freebox home-gateway
       (upgrading for this an available 6to4 code);

   3.  provisioned PC-compatible platform with a 6to4 gateway software;

   4.  modified it to support 6rd;

   5.  tested IPv6 operation with several operating systems and
       applications;

   6.  finished operational deployment, by means of new version of the
       downloadable software of their Freeboxes;

   7.  announced IPv6 Internet connectivity, at no extra charge, for all
       its customers wishing to activate it.

   More than 1,500,000 residential customers thus became able to use
   IPv6 if they wished, with all the look and feel of native IPv6
   addresses routed in IPv6.  The only condition was an activation of
   IPv6 in their Freeboxes, and of course in their IPv6-capable hosts.

* https://en.wikipedia.org/wiki/IPv6_rapid_deployment

This was ten years ago, so the Internet was less integral to people's lives (relatively speaking). Some more testing may be needed nowadays for IP end-nodes, but I'm not sure if things in the network infrastructure would be any more challenging.