aakk9999 - 12:08 am on Aug 2, 2013 (gmt 0)
The point is he said that you can use on domain level.
Hello miteshseo, I have read the thread you gave a link to above and Christopher Semturs (Google Employee) did not actually say that rel alternate can be used on domain level. Note that there is a difference between what means "using on a domain level" and "using across different domains".
Perhaps the confusion is that your examples show domains, but in the same time this "domain URL" from your example is actually also a page (which would be, I presume, a home page of the domain).
I think this is why Christopher Semturs is asking you for your B) question "Why for different content...", and this is why he was also asking you to provide a concrete example with real content and URLs.
If you read official google support page on rel alternate, they talk about the "page" (which may be on the same or on a different domain) [support.google.com...] but important is that the rel alternate should point to a translated page in other language and not just to the domain root where this translated internal page exists.
In other words, you will have to set up rel alternate on every page, pointing to alternate page of this page in other language (which may be on another domain) - rather than setting rel alternate for each page on one domain to point to the root page of the another domain (as I explained in my post above, see the example on blue widgets translation).