I said they could trade him in the offseason, just as an example to show that they don't HAVE to trade him. They could trade him now, they could trade him in the offseason, they could trade him next offseason, or they could never trade him. I don't care how committed you are to "rebuilding," there's nothing wrong with holding on to your best player.
This isn't a 'trade him for whatever we can get while we can still get it' type of situation. They probably have a minimum that they're willing to take, and if they don't get it, they'll be perfectly fine with keeping one of the league's elite tight ends on their roster.
Reports are that this situation wasn't even prompted by the Chiefs, but by Gonzalez himself inquiring about the possibility. So as a show of good faith, and maybe as a tip of the cap to the good years he's given them, they told him they'd listen to offers. This isn't even the Chiefs idea, so you know they aren't desperate to get something done. They weren't even thinking about it until Gonzalez brought it up.
If a deal gets done, its going to be on their terms.