you can consider a 3rd option, which is slightly a better version of your 2nd option. (i think this is still possible, a bit unsure)
call up nintendo customer support, if the nnid is same region (both are us for example and not us + canada combo) you can try request them to merge nnid. make sure the one retained is the one on 2ds. then sell the n3dsxl once the process is done
save data will be lost btw
https://en-americas-support.nintendo.com/app/contact

This post has been edited by kuroneko0509: Dec 8 2017, 05:13 PM