We're currently waiting to find out for certain if ABC is going to pick up Marvel and Joss Whedon's S.H.I.E.L.D. TV pilot to series, even though production wrapped almost two months ago at this point. However, assuming that happens, it might be a while before any superheroes and/or important players from the larger Marvel Cinematic Universe make an appearance (which is partly because Whedon and his fellow showrunners have been too busy to plan that far ahead just yet).
There will be a familiar face from the Whedon-verse in the S.H.I.E.L.D. pilot - not counting Agent Coulson (Clark Gregg) returning after his (apparent) demise during Marvel and Whedon's The Avengers - and the individual in question is actor J. August Richards.
SHIELDTV.net, which was the first to break this news, is confirming that Richards makes an appearance in the S.H.I.E.L.D. pilot, but is not sure whether or not he's onboard for additional episodes; nor, for that matter, which character he is playing. Whedon has always been open about the fact that his Marvel TV series "needs to be its own thing" and won't incorporate many characters from either the MCU or any comic books, so that makes it difficult to properly speculate about just what Richards' "mystery role" on the show is.
That's not to say that Richards - who was great as the street-smart demon fighter Charles Gunn on Angel and thereafter starred on the Conviction and Raising the Bar TV shows - won't play a significant role in the S.H.I.E.L.D. proceedings. However, it is a fair bet that he won't be portraying anybody that comic book fans have met in a previous form (be it on the printed page or in an animated TV series).
All the same, I speak as a longtime Whedonite when I say: any Buffy the Vampire Slayer, Angel, Firefly or even Dollhouse alum who comes back to play some more in Whedon's sandbox (like Richards) will be welcomed by me.
The S.H.I.E.L.D. cast includes Chloe Bennet, Ming-Na Wen, Brett Dalton, Iain De Caestecker and Elizabeth Henstridge, in addition to Gregg and Richards. Meanwhile, Samuel L. Jackson wants to show up as the organization's commander Nick Fury in some shape or form, and Cobie Smulders could appear as Maria Hill (though, her commitments to Captain America: The Winter Soldier and How I Met Your Mother may prevent that from happening sooner, rather than later).
S.H.I.E.L.D. is expected to begin airing on ABC by Fall 2013.