Motorcycle has:
LARGE OBJECT: If Motorcycle is on the map, characters can't occupy its squares. // Adjacent characters can be given a POWER to equip Motorcycle as if they were in its square. // Motorcycle is not Unique.
And replacement rules state:
Replacement characters must occupy at least one square that was occupied by the replaced character. You can’t activate an optional effect that would replace a character if the replacement character can’t be placed into one of the replaced character’s squares or a square the effect otherwise specifies. Non-optional effects may do so, and an opponent chooses squares for the replacement to occupy, per the Rule of Occupancy.
And 25.2d states:
When an equipped character is KO’d, replaced, removed from the map (for any reason), or equipped again; their currently equipped equipment is unequipped. A character can’t normally choose to unequip equipment. When an equipment becomes unequipped, it will either be placed in a square the equipped character occupies or it will be destroyed. Each equipment will have a keyphrase denoting which will occur.
So: can King Killmonger even activate his replacement effect when equipped with a Motorcycle?