A low-data client with a good ux would be awesome. Gossip does some of this, but it's desktop
Discussion
it should be possible for egui to be built to run on mobiles too, if the UI has been changed to fit the dimensions... i was working with an IMGUI library called Gio back in 2018 that you could do that with (golang of course)
Not necessarily gonna pursue low-data usage at the cost of poor ux. It is more like taking advantage of knowing well how nostr works to not ship code that carelessly connect to more relays and asks more events than needed.
It might be harder than you think
the lack of negation operators in the filter spec of nip-01 makes low bandwidth hard to do without a sophisticated relay side filter filter
like, just to elaborate a bit more, i've thought about the idea of a relay that if it can find your mute list, automatically excludes them, it would cost more processing so it's definitely something for a paid relay