Honestly I expect the 3DS to be manufactured until FY2020.  So I don't expect it to be discontinued until spring 2019.  Which is fine with me.  Hope it eventually hits GBA/PSP numbers.  I love it personally.  Its my favorite handheld and in my top 5 favorite platforms of all time.  I look forward to enjoying it for another year or two.  I'll miss 3D when its gone.