Interesting final line-up of songs in that Hollywood Reporter article, some of them getting a full reconfiguration, others just a few touch-ups. "Defying Gravity" seems to mostly be rematch, with Mercedes thrown in for good measure, while "Don't Stop Believing" gets just a few tweaks like the inclusion of people who were close to Finn; Will of course learned how to be a man from his student, while Blaine got close to him after they formed an alliance to clinch a Sectionals victory after the girls deserted ND (coincidentally, the picture used to represent that episode for last night's event was the fist bump between the two).
Although he was extremely successful as Tony in West Side Story, I am not sure the male lead role in Funny Girl would suit Blaine. But then again, everything in that plotline bursts credibility at the seams. And RIB would then have the satisfaction of a trifecta of Lima graduates involved in that production, even though it would be extremely arbitrary; two of them (I am assuming Santana would also play one of the lesser female roles as is the practice) is enough.
It's almost untenable that the producers of Funny Girl didn't even consider him for the role of Nick Arnstein.
Regarding Blaine development in S4 and S5, we saw various aspects of his personality emerging or being further featured, more than several other characters got over the years. It may have come in spurts but that is how the show works with its sizeable cast. By Glee standards, that certainly was development and characterization; no character on the show is truly deeply developed anyway, including those presently forming the NYC stream.