There is always value in limiting configuration changes close to starting the take-off roll but in this instance it is adding the operation of an additional fuel pump… not likely to cause an unintended issue, and in my opinion, individually confirming the operation of both fuel pumps being able to provide sufficient fuel flow on their own is far more important.I see the value in testing without the boost pump on. Is there not value in leaving the configuration you had during the runup the same as during the takeoff? Since I'm going to take off with the boost pump on, I like to do the runup with the boost pump on. I've tested the mechanical during taxi, although that's certainly not full power. I wonder if testing boost both on and off during the runup would be best?
I'm sure I've read of a crash that was caused by the boost pump causing too much fuel to get to the engine - I think it was a mooney or bonanza. I'd hate to find out something is wrong when running the boost pump during the takeoff roll.
I.e., one of the purposes of the run up is test equipment for proper operation vs just configure it for takeoff.