The idea is simply that instead of being bound by the particular type of switch that ships on your keyboard (Red, Brown Blue, etc.), modular switches allow you to change the switch type at any time.
That brings obvious value, as you can buy one keyboard and then play with your switch preference, but the notion of swapping out all 104 switches (or fewer, on a TKL or 60% keyboard) sounds like a tedious task at best. It seems that some people may prefer to employ a certain type of switch only for certain keys--for example, the WASD cluster or the numpad. (Personally, the idea of having different switch types on one keyboard sounds unpleasant, but that’s just me.)
Kaihua will offer Red, Brown and Blue modular switches. Although the company has not enumerated which keyboard makers may employ the modular switches, at least one--B.Friend--already has a keyboard (the G Master MK1) sporting them.
Although these Kailh switches will be available in Red, Brown and Blue, we presently have access only to the Blue specifications. What’s most noteworthy about these specs is that they’re nearly identical to the Razer Green switch as opposed to the standard Kailh Blue switch.
There’s no word on when these switches might be available on other shipping keyboards.