Wow, the intro to that just doesn't sound good at all after you've heard the intro from the original movie.
I agree that if Arnold was in Stallone shape this could probably work, because some of the "L. Sprague DeShit" stories were pretty good with Conan being King of Aquilonia, married to Xenobia, having to go on one last adventure to rescue her, etc. It could work if he were in good enough shape, but unless he started awhile ago and is as dedicated as he used to be, I just don't see it happening in time for this movie.
Not really sure I want to watch a movie about his son unless it is someone awesome, but really, who could that be? Unless it is The Rock, I'm not sure I care about anyone they'd be likely to pick. No Taylor Kitsch, no Khal Drogo. Hell, Thor would be ok, but I have severe doubts that he'd have the time to do it even if he wanted to.
Oh shit, I just realized, since we were talking about The 13th Warrior in another thread, if they made it sort of like that, with Conan as just the enigmatic badass leader, but a band of young Cimmerians (maybe including his son) following him and doing most of the heavy lifting, it could be pretty good with the right story and the right cast, and a good synergy between the youngsters. Might even open the door for a follow-up without Arnold if they get a charismatic character to take over after he's done.