Sorry, if off topic.
I had a discussion with my brother about comparing the spinoffs between CG and ML, and one thing worth mentioning was the timeline differences. I know I’m just stating the obvious.
There are some hints that CG coexists in the same timeline as 765pro idols (when 765pro were rookies and brought up) though probably not including Cinderella Girl Project but just 346 in general.
However, ML exists in a pretty restrictive timeline where they are present only during the timeline where the 765pro idols are top idols.
With the exception of the Movie and the ML manga, most iterations of 765pro whether it’s the anime, main games, manga, dramas, etc. almost always depict them as rookies who are brought up. Which means ML doesn’t exist throughout 765pro timeline until they (765pro) become veteran idols with a complete character development/story who can act as mentors.
This trailer along with the Movie and ML manga pretty much confirms that ML begins after 765pro story is completed and the idols are top rank. After all, the appeal of ML is that they are the future of 765pro. So, it's kind of difficult trying to assimilate with them 100% completely given ML restrictive timeline. Like mentioned before, previous iterations and likely the PS4 iteration of 765pro will depict 765pro as rookie idols and rookie idols can’t act as mentors, so ML won't exist until 765pro become top idols.
I know a lot of Japanese fans see 765's huge presence in ML as "baiting" main series fans,
That’s likely true since ML doesn’t have the popularity as CG or other idol franchises and there's so much competition. So, they need the original 765pro presence to give them some importance. Otherwise, people will just ignore them. And, I guess it also answers the question "what happens next" after 765pro reached top idol.
but I like how it gives our original idols some more depth.
Aside, for some advice giving and having ML characters idealizing Haruka and/or other 765pro idols (as seen in the ML manga and ML trailer), I doubt we will see anything else new for 765pro. (And, according to the Idolm@ster Mana Manga, Chihaya takes up photography right after her story arc before Haruka’s story arc begins. So, her new hobby started before the Movie thus before ML).
