I think they should at least make official extensions full compatible with opera, extensions that will not slow down the browser or what. Extensions that everyone can trust and that perfectly go with the opera UI. Auto refresh doesn't, for example (Horrible font/color when deploying, not the same reload logo than the real reload logo...).
But if this type of discussion has been going on since a while, that mean that many people want that features back. So are the developpers blind and deaf, or don't they give a fuck ?

"What happened to X" I didn't want to put things that were already there, I have nothing to say about them

I see two answers in your post :
The things that "can be done with extensions" : Okay so that mean that the huge amount of missing stuff in opera 15+ is missing because there is....extensions for it ? And so it will not be added ? Because if that's okay for the "Reload every X seconds" and "Open with X program", why not removing the bookmarks, the tabs, the menus, the settings and the download manager ? I mean, anyone can make an extension for it, so why should the developpers work on that kind of stuff ? That's a shame.

The things that "are done and won't come back" : That's not even an answer. I mean, I know it's gone. I don't want to know that it will not come back but WHY it isn't coming back. Was the IRC chat in Opera 12 by mistake ? No ? Then why is it "not coming back" in opera 15 ? It was so useful !! Same for the mails and the P2P. And I'm not even talking about the RSS feedreader.

Opera 12 was a browser that could litterally do everything. Now in opera 15+ you need "extensions", because "good things are gone and won't come back", said the developpers. Great.

I'm actually using, since opera 12.x does no longer support most of the internet, the shitty opera 28, or 29, no idea.
Opera 12 was my favorite browser for many reasons, but especially for these 10 things :
http://www.ghacks.net/2012/05/17/10-things-that-opera-does-that-other-browsers-dont/

When I first used opera 15 I almost puked because nothing was there. Now that we are, fifteen versions far from the 15th, there is still almost nothing.

So my question is,
you see, the 10 things that are listed. When are they going to come back ? In how many years ?

1. Tab stack

2. Your own keyboard shortcuts

3. IRC

4. Integrated opera Mail

5. Notes

6. Reload every X seconds

7. Open with X

8. Downloading/Seeding torrents

I maybe the only one in the world asking for this, because if I weren't everything in that list would be already there. But I want to know.