These seem to be the go to upgrades. My forum search showed up threads on this but nothing newer than 2015 so I wondered if there were more options now. I guess, if it ain’t broke, don’t fix it.
Lakland has their own set of pickups to replace the MK-1s:
LH3 Pickup Upgrade for Lakland 44-01 and 55-01 Basses - Lakland Bass Guitars
I actually have a pair but never got the chance to install them.