This seems a stretch, as the colonies in the West Indies were all Spanish, not English, prior to 1648. Merchant ships of many kingdoms in Europe carried cargo to the Spanish colonies. And I have never heard of any pre-Jamestown planning by the Crown for slavery in English colonies, but I’d be curious if you can provide any documents of it.
Also I find it absurd you never heard about Walter Raleigh, Charters/private passages, heck you never heard of the Roanoke Colony, that right there suggest planning stages. This before 1585.