I think there are no solid definitions of 2.0 or 3.0.
NXT called itself 2.0 which I think started the whole "generation" fuzz but I'm not sure there are actuall definitions.
If we see non-POW coins as 2nd gen then NXT was by no means the first 2nd gen (unless we only count 100% non POW coins and no hybrids). If we see transparent forging as 2nd gen then any other advanced feature could be 2nd gen as well so there is no way to tell where 3rd gen starts (leaving aside the fact that transparent forging is afaik not yet implemented).
I think if POI works as intended then it could be considered 3rd gen as it would be another improvement over the existing algos.
So it would be...
POW -> POS -> POI
...which would make sense to me but again...hard to say.
Could also be POW -> POW/POS -> POS -> POI.
Asking me I think the whole generation question is a huge amount of bs. Who cares ?