One of the poster-child cases for the outside view (mentioned by Eliezer, no less!) dealt with students trying to estimate completion times for their academic projects. And what is AGI if not a research project? One might say AGI is too large for the analogy to work, but outside view helpfully tells us that large projects aren't any more immune to failures and schedule overruns :-)

Thus, you would be perfectly within your rights to say that most people predicting AI believe that it will arrive long before it actually does. You can use the outside view to deny timeframes and specific projects, not the basic possibility of transhuman AI.