I just read you and I found it very interesting !
I have never seen Mika as "just a singer" either. He is a complete artist with crazy creativity and huge imagination, and I think he has this need to express himself through art.
So of course he is a musician and a singer, but I do not think we should lock him up in one box, "he has to make music and just that." (I do not say that in relation to you directly !!) Especially when you see how talented he is in his other projects too ! Watches, clothes, bottle, pens, all his drawings... And also Casa Mika, which has been a big project and a huge challenge for him, and I think that he completely nailed it, it was fantastic !
So personally, if he had to make or play in a movie, I would not mind if he thinks it's a good idea or if he really wants to do it.
For the musical, if it's one of his dreams for a long time I hope he will one day find the time to realize it, (even if it's already a really really really busy man !) and I'm sure it could be magical <3
And I'm completely sure that he will never give up music, we all know how important is it for him ! ^^
(I'm sorry for my probably bad english haha ! I try to do my best ! )