Sidewinder cant have a double rack as it can't fit a size 3, so it will be limited to a size 1 and 1 type controller. Nothing changes. The hauler and adder will get a small buff, but again not a big deal and they could probably do with it.
The big three will only be able to fit the size 3 in a size three, but only have 2 types of contollers, they want four controllers they will need to fit in a size 7, massively reducing the amount of cargo space they have. Infact it will give bigger ships less flexibility, but giving medium ships slightly more which is what is needed in my eyes.
off topic really .. but say I'd like to fly my Sidewinder more than I do (example). As we're talking about a brand new idea, rack sizes are somewhat arbitrary at this point, so why not also add some flexibility to smaller ships at the same time, reducing incentive to grind? Start a thread on and point me to it? /off topic.