This is not bold. It's dumb.
1. You are saying that Octo will have a popularity level on par with a mainline Final Fantasy, the face of the JRPG. No.
2. Kingdom Hearts 3 is the second most popular RPG series. It will not reach 6 million copies.
3. Dragon Quest 11, the father of the JRPG, will not reach 6 million copies.
4. These games will/have been released on multiple platforms.
Octo will finish somewhere in between 1.3-1.6 mill. There is no way in hell Octo will come out and eclipse Decade+ strong IP's in one installment on a single platform. If it is not Pokemon or Final Fantasy, a JPRG's chance at over 3 mill is zero. Over 2 mill is smashing success. Just achieving 1 mill is a victory. For some, 500k is milestone.
* Pokemon is ignored on purpose because though it is a JRPG, it has ascended past the confines of its genre.