Assuming R+L=J what do you think rhaegar would have named jon
“Mothers can name a child before birth, or during, or after, even while they are dying. Dany was most like named by her mother, Tyrion by his father, Jon by Ned.”- GRRM
I think it would have been a male version of Visenya. Rhaegar's other kids were named for the conquerer trio so it makes sense
what are your theories