"Is there anything new that you couldn't do with tables 15 years ago? Or are they not cool enough?"
For extremely simple layout then mostly, no, but only in the same way as you might say about higher level programming languages such as C/C++/Python/Java etc,
"is there anything new that you couldn't do with assembly X years ago ?"
You can mimic a fair bit of CSS layout with tables but, really, would you want to ? For some rather old perspective on the basics of this, you might want to have a look at Douglas Bowmans presentation 'No More Tables', if you haven't already (link to a video of the 2006 one follows)
Tables are very useful and for some data they are almost certainly the best choice, but they are not the answer to page layout in general.
As for the extensions - i've only had a quick look at the documentation on Operas site about them but there do seem to be some (potentially) very useful bits.