I definitely think Roko will be a solid backup - it's not going to be a 1a / 1b case like last year's point guard situation kind of was, so I'm glad that the better point guard is going to log more of the minutes.
But people are talking about Roko possibly being a bust, and I honestly don't see it happening. Roko really doesn't fit the mold of the average European player - his tendency is to slash, his handles are supposedly legendary, and apparently his shot needs work. I think the fact that his game is more NBA-suited decreases the chance of a bust. That's just my two cents though.