Of course. Even with the SDK, people are still going to make sure that Installer.app works along side of official apps so that unlocking software can still be used.
I'm definitely going to have my iPhone jailbroken and have the SDK at the same time. Just think, normal official apps as well as SSH and other wicked applications
Even with Installer.app the possibilities seem endless with new apps rolling out every day or so. Just think what it will be like when large companies start producing apps for the iPhone too!