I'm trying to avoid making those sorts of comments about his future.
Karlsson will only be 20 next season, we still haven't completely seen how he'll respond to an 82 game schedule (although I guess you can count the 12 AHL games he played) and the highest scoring Sens' defenceman in recent memory was Redden with 50 points (albeit in fewer than 82 games) in 2006 when the Sens scored 314 goals.
I recall when Gagner ended his rookie season on a high Edmonton fans were gushing over him and projecting 80+ point seasons in the immediate future. Development/projection doesn't necessarily happen in a linear path and there will be ups and downs, even with Karlsson's tremendous hockey IQ.
I'd be very happy with 35-40 points from him next season with improved defensive play. That's roughly in line with the top-end production from Sens' defencemen over the past few seasons and IMO about all you can ask from a 20-year-old. Greater production certainly isn't out of the question, but I think it's too much pressure on him to project him as a 50+ point guy as early as next season. If it does happen, that's just gravy.
Anyway, **** next year, we're in the playoffs.