I will watch Ewan McGreor as Obi-Wan in anything. I picture it as something like an old episode of Kung-Fu in space. Someone else as Obi-Wan would be an uphill battle.
Unless of course the give us The Young Obi-Wan Chronicles that follows a young padawan Obi-Wan on his adventures with his mentor Qui-Gon, also portrayed by a younger actor.