If, as you say it was not so hard to do, why the core team doesn't did it already....
Here is a reply as to why the devs don't want to use it http://forum.joomla.org/index.php?topic ... icseen#new
Basically it is a backward compatibility issue.
Is it safe to do this in a working website?
It will not damage the structure or the databases?
Is it possible to this with the next versions of joomla?
I would completely test this first, before i used it in any production site.
It doesn't change the database 1 drop. The parent_id field isn't being used for ANYTHING so its safe to use.
The demo site I have up at http://joomla15.wpmdev.tzo.com/
is running what will be the next version of joomla, so yes, it works with the next version.
My uneducated newbie guess as to why the developers haven't done this yet is that the current system of sections and categories just isn't how things *should* work. Sections are categories in concept, when you think about it. That is why in 2.0 they are going to do away with sections and allow for subcategories. There is a way things *should* be done, but doing it the *best* way will require a change in the overall way the system works (no sections) . Regardless of what the *best* way to do things is, it can still be done with the system as is. They just want to wait and do it right. But this is just my guess.
Not all of us can wait that long. In my research, I found very little on how to make the system do this. That's why I have posted how we did it. If someone else wants or needs to do this, now they can find out how to do it. If the devs look at it and say, what the heck, lets put it into the next release, that cool too.