When I was on the Excel team the kernel devs I talked to knew their stuff and were of the highest quality. More importantly they cared and stuck around to see the consequences of their actions.

The windows org has a reputation of being dysfunctional although I never personally observed this, and personally think even if it were true it would be in the higher level parts of the stack.

Kernel dev was my original dream but I fell in love with Excel during my internship. I definitely think you should go for it.