I believe Roslovic will need some sheltering (at home when it's possible) early into the season. But I also believe he will be clearly the best option for second line center. He really impressed me late last season and in the playoffs..enough to believe that he can handle the defensive responsibilities of a NHL center. He has the speed, IQ and skills for that and seems like a very responsible player.
While Little and Lowry may still be better defensively the one thing Roslo is better at is utilizing skills of his winger. In a bit similar way that what Statsny did. You can see that already from his play as a winger. So if Jets plan to have some combination of their young skilled wingers (Laine, Ehlers, Connor) in the second line I honestly believe Roslo if by far the best option. Or course he will need to earn that spot in the camp and preseason but I think he will.
You could of course say that Roslo need to earn his way up in the lineup and maybe start as a third line center. I don't really care what line numbering Jets use (remember the Statsny line was called 3rd line) but if they want to get most out of the lineup then Little should play with more defensive players and Roslo with more skiller wingers. Roslo will get more out of those skilled wingers and Little should be better in a more defensive role.
This is my hope as well. Start out the year in training camp and preseason giving him every opportunity at 2c with talented wingers, then shelter him a bit if needed early in the year. I think he can run with it, and if he can we are set for years at C.