I’m constantly running into multiple groups that address the same subject. It would be nice if I could combine those so I saw all the posts in one place. For example, all the forums that are discussing UAPs it would be cool to just look at a single thing that combined them all. 
Yea, honestly I think this is where an app can really shine vs using the website (currently).
Another example: Formula1 communities are on lemmy.world AND lemmy.ml. As a user and member of both, I don’t care which one I’m seeing/engaging with, I would rather they be grouped together so I can see the content from both at the same time rather than having to go to each community.
I guess this would be akin to Multireddits (I think it was called?) where you can pick and choose which communities you are subscribed to are grouped together. Meaning you could also do this for communities that don’t cover the same specific content, but a more general category, such as “computers” and have all computer related communities you subscribe to in that group.
Yup, I remember Reddit had something like this. 
This is something I think shouldn’t be specific to a single app. There’s an issue requesting this functionality on the Lemmy GitHub repo: https://github.com/LemmyNet/lemmy/issues/818
If you are interested, it would probably be good to leave an upvote (👍-reaction on the first post in the issue thread) for that issue and maybe a comment detailing your specific use-case and any ideas you might have for how it should work.
There’s an active issue on the lemmy GitHub about this. https://github.com/LemmyNet/lemmy/issues/818
(Mlem dev here) Custom Feeds is something that’s on our radar. In an ideal world, this would be implemented on Lemmy’s side so that it’s available across all clients and not just Mlem. For this reason it’s not on our immediate agenda right now.
I believe this is closely related to how we manage numerous communities that focus on the same topic. It’s likely that many of these communities have little to no activity. Eventually, I suspect Lemmy will face a real problem with this given no cross community/instance admin role.
wound mouth window blood view suggestion move again chief event love water though lip branch step chest take tree destruction sea button violent second level authority damage gun chance poor earth help pain table daughter much gun help brick electric kick word steel word finger taste birth give political birth
person cork under dependent healthy butter finger day deep yes paper knife mine not quick letter wing seat different bee nerve smash pig porter side point blow digestion plane line wire hammer happy nut blue instrument attraction journey safe nut shirt get ice liquid clock protest cow walk square for
round against love young protest work crack building station tendency island sock advertisement send note together chance oil then true through get wool self dependent place forward copper plane business as touch smoke discovery bulb narrow through story degree horn by damage horse cat fold direction only sweet ticket skirt
smooth polish wash to line sign test keep send future you son regular growth ship cut bent pump chalk enough help dark trick book limit net out iron selection than degree tray top together walk trouble selection leather crack month loss month square motion balance death discovery heart ant run
wave market mountain every throat time grain adjustment quite young trouble memory brother motion fixed boiling kettle smooth thick thin mine bucket play development discussion act trouble respect out thing warm cold out hope forward full group prose air cushion chalk angle sand near debt do statement clean substance throat
smell bite free warm cut let control change dark twist cloud then opinion box fork unit front west observation trick screw boiling fold far ring door invention company pump clean happy grey poison stomach wax hope keep process deep old produce teaching sudden long account station first help but soup