Thanks for the quick response.
Well one site could have a Tweet button & another may embed specific Tweets (instead of having them Tweet about the site/page if they feel like going out of the way to do it or linking to each Tweet & browsing away).
Now the Tweet button both links to twitter.com/share & the JS widget at platform.twitter.com and I understand now that I see the CDN’s website with a public page about their IPv6 status but I couldn’t find anything for the main Twitter domain specifically so I asked here.
Embedding (as you know) would need to use api.twitter.com (and possibly others) which is not hosted elsewhere.
So could you answer about twitter.com, api.twitter.com, etc. or should I assume that dates haven’t been set (or able to be announced) & I should plan without IPv6 support?