With respect to Alan's suggestion that a timer could be programmed that would automatically switch between RPMs #1, #2, and #3 (in Castle Creation's Set RPM mode) so that the RPMs would increase during the flight, that wouldn't be too difficult to do. It is easy enough to select among the three RPMs with a timer because they are defined by the % of full throttle. (It might complicate the finding of an RPM that would serve as a warning at the end of flight time; currently I program RPM #1 if it is not in use and RPM #3 if it is.) It would take longer to make a timer that allowed one to switch on this automatic increase in the Set RPM mode only when desired, because it would require a new circuit board.
However, there is no reason why this automatic increase in RPM can't be accomplished in the governed mode of any of the ESCs that support it. In particular, that capability already exists in the FM-9 programmer, through the "Compensated Throttle" mode. It allows one to choose the desired % of throttle (in 1/2 of 1% increments or decrements in the latest firmware), from 15% to 100%, but it also allows the user to choose how much the throttle will be increased during the flight (originally designed to compensate for the decrease in power due to the battery voltage declining when using an ESC without a governed mode.) There are 16 choices to make when choosing the "compensated throttle" mode:
Choice + at 30 sec + at 1 min + at 2 min + at 3 min + at 4 min + at 5 min
0 0 0 0 0 0 0