Thread detection is a function of the reader, and either news or mail readers may have threading capabilities, but they're not guaranteed. News offers a better system of permanent citation. News archives can appear via DejaNews or simply by any site choosing to never expire articles in the newsgroup. Actually, most of the discussion happens on comp.text.xml, and there is a group for Microsoft sycophants in the microsoft.public hierarchy. The next step is for one of the people noting the division to post an article asking whether a split should occur.
Informal discussion occurs, possibly cross-posted to news.groups or groups on related topics.
If the vote is favorable, a news adminstrator creates the group. I think that the current c.t.x volume is not excessive, which explains why an XSLT-only newsgroup has not yet been created. That's a function of the reader. Articles arrive asynchronously from The Net and are stored in order of arrival. It is common to have early replies arrive before the beginning article in a thread.