I really don't see the point of worrying too much about it right now. People get too caught up with trying to read between the lines of every single utterance that escapes Danny or Rondo's (or Brad's) lips, magnifying the significance of every breath tenfold.
It's not in the interest of _anyone_, not either side, to commit or show inclination one way or the other in advance.
Well, I don't think it's in the interest of the Celtics to just wait until next summer to worry about whether or not they can re-sign Rondo. Because by then it'll be too late to get a good return for him if it turns out that he's interested in signing elsewhere.
If it turns out he's interested in signing somewhere then that's probably where they will send him.
They aren't going to be able to just arbitrarily trade him to just any team because pretty much no team - other than a contender who's current PG gets injured and is desperate for a top PG in order to make a playoff run that they've already bought in for - is going to trade a lot for Rondo if he won't sign an extension because they would just be purchasing the same 'dilemma' that you assert the Celtics are facing.
So they aren't likely to get more now ("a good return"), trading him to a place he doesn't want to go than they are later, trading him to a place he wants to go.
The only motivation for jumping the gun and trading him now, at a value discount anyway, would be for a target of opportunity. If a specific trade is especially appealing to Danny and is only going to be available this summer. Or the above mentioned scenario where a team has already committed to contending next year but finds themselves suddenly in need of a Rondo caliber player.
But both those are extremely unlikely.
The only path towards keeping Rondo long term runs through free agency (because that enables the longer contracts and possibly bigger money and possibly a no-trade clause). And there is no real advantage in returned value for trading him now versus trading him next summer.
So, again, all signs indicate that it is not likely he will be extended OR traded this summer. And that more likely things will happen next summer.