On Reddit, just from this month alone, there have been some great AMAs that I personally think HN would be great participants in:
Stevin Levitt from Freakonomics http://www.reddit.com/r/IAmA/comments/18tp7t/i_am_steven_levitt_author_of_freakonomics_ask_me/
Bill Gates http://www.reddit.com/r/IAmA/comments/18bhme/im_bill_gates_cochair_of_the_bill_melinda_gates/
Peter Sunde of ThePirateBay http://www.reddit.com/r/IAmA/comments/187iwo/i_am_peter_sunde_cofounder_of_tpb_ama/
SpaceX Software Engineers http://www.reddit.com/r/IAmA/comments/1853ap/we_are_spacex_software_engineers_we_launch/
Do you think this this is something we could start on HackerNews?
Why would I want HN to be a megaphone for Famous Joe Blow X when I'd much rather have him actively participating and helping out in the threads with the rest of us?
This is a very bad idea in my opinion. Since I have no clue how to run a busy site, that means it'll probably happen. :)