That ray of light could mean one of two things:
There is a slim chance that Quinn actually survived and turned out fine
Or
That Carrie was making the right choice in letting Quinn go
I think it was the second choice they were aiming for but I can understand how some people can see it as the first choice. My brother said the same thing as the first option.
Otto's offer was weird since we barely got anything to insinuate that he wanted Carrie in that way. Claire Danes has such good facial features and motions that you could tell she was just as confused as the audience. Carrie's got time to think about it and I think she should take it. That way we might get something sort of different for season 6 unless they really wanted Carrie back with Saul.
That is something I wouldn't mind also. Those two, when paired together seriously, are probably the best in the business and that's why Saul wants her to come back even if she doesn't know how to solve these new threats. Carrie will always find ways to take down the enemies whether it's due to the plot or otherwise.
The season as a whole was ok-good for me. The major gripes I had were, again, how convenient some of the actions were and how the plot demanded for stupidity.