Good question .

The SD1plus will be using 4.0 . So Ketron must believe it is a winner .

I like the features of OS4.0 ( I even suggested idea's that were implemented with 4.0), but I like the sounds of 3.0 .
AJ told me that he was developing 4.0b , so that the SD1 owner will be able to use 3.0 sounds with 4.0 feature's . As of today , I have not seen 4.0b . 4.0b would make me happy !

It's totally up to the end user to decide .

Dano