Why does it need a reboot? There's no need to follow any of the continuity of the first three while still being a sequel. It would be cool if TLJ was the head of the MIB or if Will SMith was now the grumpy old partner.
It doesn't need a reboot, but it's Hollywood so they'll take all the extra $$$ they can get. With MIB, I doubt the demand/anticipation will be there to garner a big enough audience for opening weekend like The Forced Awakening. I'm 99% sure it will bomb.