A Maximum PC article brings us the first possible details for the unlockables being worked on for the Engineer class in Team Fortress 2.
We noticed in last night's game that Valve is also tinkering with upgrades for the Engineering class. While it's not concrete that these additions will go into the game's next Medic-friendly update, Valve is nevertheless looking at adding upgrade options for the Engineer's teleporter and dispenser. The former, when upgraded to Level 3, would reduce teleport recharge times from ten seconds to three. And a fully upgraded dispenser would heal all around it just slightly slower than a Medic--akin to Shadowrun's Tree of Life.
I'm not too sure about that dispenser bit that they have, as that is essentially what it does already. We'll have more on this as we receive the information!

Update: Valve's Robin Walker confirmed with us that they are indeed working on the Engineer's unlockable weapons. However, he states that they may very well change before their final release.

Honestly, I don't believe it.
Because all the medic unlockables have certain tradeoffs, so they're not really upgrades.
But a level 3 dispenser ot teleporter sound like a simple upgrade, without tradeoffs. So they would have to be very expensive to be balanced.