I don't think that shadowkeeper allows more than one kit, anyway. If the first class of your dual has a kit, you could change it, but not add another.
I suspect that the way character files are stored, only one kit is possible.
Of course, that doesn't stop you from adding the innate abilities of as many kits as you want. Hmmmm...Kensai+Swashbuckler+Assasin+Monk+Barbarian ...that's just wrong.
Personally, I am fond of Kensai/Mage multiclass. I WISH I could have a Kensai/Sorceror multiclass

Ah, well