I've never noticed my Cherry blue or brown keyboards break in. The spacebar on the one stopped squeaking over time, and the scrapiness of some of the switches has faded, but I never noticed any change in key feel at all. If there was a change, it was too gradual to detect without having an unused keyboard as a comparison. That said, my perception of blues can change several times a day, from too light to too stiff!
It does feel like my Tactile Pro 3 has broken in – it gets very little use, but it's not as balky now as it was when new. I have no idea what blue ALPS are like new, as my blue ALPS board feels good enough to be new even though it's old and heavily used.
I dread to think what Acer boards are like new, as they're a menace even when they are well worn!