Photoshop into lightroom as to after effects is to ??

This is a user-to-user forum, so you might be better off posting in the After Effects UserVoice forum as a feature request: https://adobe-video.uservoice.com/forums/911311-after-effects

That being said, what exactly would you want this app to do? After Effects isn't made for video editing like Premiere is. And for that, there's already Premiere Rush which is a light and cross-plaform editor which can even use some motion graphics templates. There's also Creative Cloud Express (formerly Spark), which is very mobile-friendly, has some great type and composition tools, and even allows for some simple animation: https://www.adobe.com/express/

Creating a light version of After Effects would be no small feat, and given its wide toolset, what exactly would you expect it to do? A compositor (which After Effects began its life as), motion graphics, character animation? Regarding the character animation, just this week, the Character Animator team introduced "Starter Mode" to get people going quickly with that toolset: https://pages.adobe.com/character/en/starter#:~:text=Starter%20mode%20is%20a%20free,been%20this%20easy%20or%20fun!

I think it would be nice to have a mobile app with motion graphics capabilities, but this is a rabbit hole that would be very, very deep to go down.