Not to be confused with M9, M9+ came out to solve a lot of hardware issues that exist in M9 and it adds some valuable features like fingerprint scanner, it’s stuck in official marshmallow and has no LineageOS nor any custom rom support that I could find (Except for a discontinued CleanSlate Lollipop rom) so having /e/ would be a breakthrough for the device
CleanSlate rom: https://forum.xda-developers.com/one-m9+-me-e9+/one-m9-general/rom-cleanslate-1-0-world-wide-edition-t3120017