I'd be sort of surprised if the powers that be let this move forward in the old timeline. My guess is that they would look at the popularity of the recent movie, the lack of popularity with the last two TV shows, and think that it would be a better bet for a new TV series to stick with the new timeline.
It could be a rights issue. Maybe the rights to the movie timeline are held by the movie people and they don't want anyone messing around with it and potentially causing issues for future movies.
So the old timeline is "safe" for a television show to mess around with.