I don't know if BeOS was too new conceptually. I think a lot of it at the time was that it was just incomplete. Limited or no printing. A slow and incomplete userland networking stack (later replaced by a more performant BONE stack). Incomplete and missing APIs. Single user, no real concept of multiple users.

I absolutely love BeOS - it remains the pinnacle of user-focused computing for me - but I think it would have been a tough job to base another commercial OS on it. We'll never know what could have happened, but Apple probably made the right choice in buying NeXT.