I would hope that NBC/UOR puts up the bucks for a "larger" , well known celebrity. My guess, it will probably be current SNL cast members, as they work for peanuts at NBC and are starved for publicity.
I know someone brought up the issue of Jimmy Fallon becoming out dated..I think who ever they use as a "guest" probably risks an even higher chance of becoming obsolete. Can you imagine if this ride was built in the 90s and Pauly Shore was the guest?