I agree. Ronaldo scores tons of goals anyway from his current position in left attacking mid, and Bale seems to have no interest in playing "left winger" anymore, so there's no reason to move him up front. The system Real Madrid has used to great effect over the past few years has also been reliant to some extent on using Ronaldo's runs down the wing to get the ball into the opposition half and attack quickly in transition, although it's always possible that Ancelotti plans to switch to a less counter-attacking style.
I think Bale will probably be used as a right sided attacking midfielder who cuts in a lot to shoot and dribble (an 'inverted winger' if you will). Watching Tottenham's games this past season, the "cut in to shoot at the top of the box with left foot" move was one of Bale's favourites and he scored a ton of goals that way. Di Maria also loves to do that but has been much less successful at it lately.