Whole idea is weird and as of now its lacking features. Like no ability to look on the other instance local feed without registrating there (at least not in apps i use). Also needing to type whole adress with instance name if you want some community from other instance is unhandy.
Also, as far as i understand, there can be the same communities on different instances, so you could subscribe to, idk, cat community on lemmy.ml, but not see anything from cat community on lemmy.world. If its true its kinda stupid, i think there should be a way to associate comunities across fedarated instances.
Hell, even registration is kinda messed up. As lemmy.world shown, you easilly can sign up on overpopulated instances which would drop several times a day. Not sure, it probably fixed for now, but that was a problem when i started.
So far i like the idea and want it to succeed and become popular. But with how elitist people here are usually towards users from other platforms and with overall roughness it kinda seems unlikelly. Maybe it will change when current apps get better, or reddit app developers make versions for lemmy, idk.