I'm pretty new on here but am also looking forward to the museum.
As far as I can tell, they are going to try hard to balance Tintin out with the rest of the work Hergé did, and more. I found an article on LeParisien.fr
The director of the museum, Laurent de Froberville, says that although Tintin will be central (it would be hard to have it any other way I'm sure!!), Hergé's other work, not just in cartoons but also in illustration and 'publicite', which means advertising, will be on display: it will be really interesting to see this lesser-known side of Hergé's work.
The director also says that there will be a 300m2 space exhibiting work by young artists, so that the museum will have a finger on the pulse of contemporary comics.
Of course it all comes down to Tintin and it looks like they will be taking great care of the original works, as the director explained that the lighting will be carefully regulated to provide a suitable amount for viewing, but not so much that the works are unduly damaged. The exhibitions will also rotate every four months so as to further protect against any light erosion, if that's what you call it.
Anyway, I thought that might be interesting to some!