Now that everyone who is likely to see the Love Live Movie most probably has, I’m going to put down my thoughts on it.
While I enjoyed the movie, it was disappointing and lost a lot of the potential it could have had. It felt like they had been planning to make a 3rd season, then during the initial drafting of the seasons storyline, realized that the voice actors contracts would expire before they could complete production and so used the basic outline to make the movie. This resulted in some quite jarring scene cuts, time jumps and lost story opportunities.
For instance, the New York trip arc could have run for 3 entire episodes, instead of the approximately 18 minutes we got in the movie.
The movie could very easily have been a full 13 episode season with the New York arc running from late 2nd ep to late 5th ep (while including Wonderful Rush as an insert song in ep 2) and the school idol scouting/Akiba live arc lasting 2-3 eps near the end of the season, perhaps eps 10-12. Finish the season off with Sunny Day Song, then lead into a movie.
The songs from the movie we got could all feature throughout a 3rd season:
Wonderful Rush – ep 2
Hello, Hoshi o Kazoete – ep 3
Angelic Angel – ep 5
？←HEARTBEAT – ep 7
Future style – ep 9
Sore wa Bokutachi no Kiseki – ep 11
Sunny Day Song – ep 12
Start the movie with the final μ's show of Bokutachi wa Hitotsu no Hikari as a lead into the 3rd Love Live before showing what the Otonokizaka High Idol Research Club is doing now that Nico, Eli and Nozomi have left (eg, Pretemps could continue as is with Kotori, Hanayo and Honoka. Maki could move into Lily White with Rin and Umi to replace Nozomi while BiBi dissolves and Yukiho and Alisa form their own group. Maybe also have an arc where Tsubasa tries to recruit Honoka into a now pro A-RISE :3).
More importantly, the movie could introduce the Sunshine girls. At least two of the girls from Sunshine would likely be in Tokyo at this time. One, Riko, transferred from Otonokizaka High, so should know at least some of the members of μ's. Another, Chika, is a fan of μ's, so is very likely to have gone to their final live. At the very least, Riko and Chika could have been introduced in a movie following a 3rd season. Then end off the movie with shots of Uranohoshi Girls' Academy and Uchiura, perhaps following Riko as she transfers there with Kimi no Kokoro wa Kagayaiteru kai? playing in the background.