No good idea to end it
The 11th season adds a few storylines to wrap things up (Niles and Daph get a son, Marty marries, Frasier leaves, etc).
Not only they all seem tacked on, they just do not give these characters the satisfactory arcs and endings they deserve.
These are such big life event clichés that seem uncharacteristic for this peculiar gang, and they feel forced on us to signify the big change that the authors believed was necessary to end the show.
Only, such change ruins and betrays the show's core, which needed this cast to adapt and succeed, not to revolutionize their lives at the last moment and abandon this world.
Frasier started as a mess, who abandons his life in Boston to struggle with his father and with his love life in Seattle. By the end of the series he finds a balance, solves these issues, builds a new life so he...abandons everything again?!?!?
Even if they all have their neurosis and problems, they are all clearly happy to live together in Seattle and to rotate around that apartment. It is their home and they love each other and this life.
The end goes against this established core: instead of showing how, after all these years, they have finally found a balance together, the writers decided to have them all move to a completely new chapter.
Quite a crappy end for a show about the Crane family life in Seattle, and an awful result for two top psychiatrists.