The TL:DR version:
1) its gen 9 cuz I say so.
2) Nintendo handhelds are always successfull, it ll still sell well even after 7years
conclusion:
its both a handheld and a homeconsole, so it ll sell like both combinded.
= 160m+ sales.
Thats basically what The_Liquid_Laser wrote in OP.
Its bold, and hes not the first to think the Switch could sell like a combination of both a homeconsole + handheld.
I personally dont think the switch will sell that much, but I guess time will tell.