Nathan Fillion is a staple of the geek world. Marvel is a staple of the geek world. It only makes sense, then, that Nathan Fillion teaming up with Marvel would cause some sort of rip in the space-time continuum out of the sheer anticipation of it all. Which is why Fillion's gotta know what he's doing to the Internet by dropping hints that he's making an appearance in Guardians of the Galaxy.
Professional geek god that he is, Fillion recently made an appearance at Saint Louis Comic-Con. It was there that someone asked him if his face is all up in this summer's Marvel film Guardians Of the Galaxy, and he responded with this:
Wanting to get a part? Or maybe did? I'm just saying... maybe? Maybe you'll be surprised? Maybe check the credits of the movie when you watch it.
Copy-paste this into some sort of textbook on celebrity teasing and tip-toeing, please, because this guy's obviously a pro.
The question was tossed his way in the first place because Fillion happens to know Guardians' director, James Gunn, having worked with him in two films previously. They also of course both know Avengers director Joss Whedon quite well.
Whedon already threw buddy and former Angel star Alexi Denisof into the end credits of Avengers, so another Whedonverser making an appearance in the end credits of Guardians wouldn't be anything new. And if this is true, chances are it'll be a cameo the Internet'd get a kick out of for a few days and gif into eternity — unless Marvel decided to just bite the bullet and throw in an easter egg of Fillion as a forthcoming Marvel superhero. That last part's unlikely, given what he said just this past summer (when Guardians was filming) about the possibility of booking a franchise:
I have two months off a year, and it's not that you can't shoot a movie in two months, but if you think about after ten months of a grueling schedule do you want to spend your only vacation working only to go back to a ten month schedule? That would make it 22 months of working. That's a tough stretch. I like vacation. I don't like go, go, go. I like sitting at home, I like traveling, I like being with my family. I like relaxing a little bit and I need that time to recharge.
But rest assured: If it happened, your Internet would break.