Probably when they start making more relevant blockbusters. I love FC and really liked DoFP, but they feel dated, especially the latter. Comic book movies that would fit more at home before TDKT and the MCU.
Which is why I am curious about this new FF reboot. They sound like they are making the Sony mistake with TASM series, without the brand recognition as a safety net.
They also lost the merch sales for Spider-Man which is why there is a crisis. I am not sure if Fox has those for FF, but I'd assume they do have them for X-Men. Thus making those films far more potentially lucrative.
Which is exactly why Marvel stopped allowing X-Men movie merchandise to be made. There wasn't any merchandise for DoFP available when that film released that was connected to the film*. Fox gets merch money, but Marvel no longer mass merchandises anything Fox puts out. Therefore, Fox does not see merchandise revenue from their Marvel adaptations.
*DoFP had Carl's Jr./Hardee's toys, but fast food toys are actually considered advertisements, and film tie-in toys are payed for by the studio. They lost money on those, in other words.