I'm actually hoping the joomla 1.6 makes SEF native no matter what extension you are using.
Already Joomla 1.5 creates FURLs for other extensions. But this is limited by nature. Joomla does not know how a component creates an URL. E.g. Sobi2:
From where Joomla should know that a Sobi2-URL has a part which is called "sobi2Task"?
From where Joomla should know that if "sobi2Task=sobi2Details" the details view of an entry is shown and the title of the shown entry which is stored in one of the Sobi2 tables, which Joomla does not know, has to be used to create a search engine friendly URL?
Same with the category names. From where Joomla should know when and how to create a URL with the name of a Sobi2 category?
You see, it is not possible for Joomla to create FURLs for 3rd party extension as you expect. Joomla already "hides" the Itemid, because this is a known part of the URL.
And this is also not possible for any SEF component. Each SEF component needs a specific file for each component where the "rules" for creating SEF URLs for a component are specified.
This is the same with Joomla. If the author of a 3rd party component writes a Joomla router file which specifies the rules for creating the FURLs, Joomla uses this file to create search engine friendly URLs. This is what SobiSEF does. SobiSEF is a Joomla router file for Sobi2 component to create SEF URLs for Sobi2 without the need of a SEF component - just Joomla native.
Trinity