The MacBook Pro trackpad doesn't support the levels of touch pressure that would make a stylus usable.
The Pencil has the pressure sensors (multidirectional, too), no the iPad Pro -- right? If that's the case, it could potentially work on the new MB/MBPro trackpads.
They'd have to get around the chance that a Pencil press would invoke a trackpad click. But, maybe it could know that the Pencil is touching, and then disregard presses accordingly.
Seems like this would be easier on a Force Touch trackpad than an older mechanical one.
(there's also my opinion that drawing on a blank piece of glass makes less sense than drawing on an iPad because of zero visual feedback without an underlying display, but I'll set that aside)