I haven't seen anyone mention this yet, but the biggest feature for me would be an automatic redirect to your current instance if you click on a fedi link to another instance
It's annoying when someone links a post from another instance, and I click the link but I can't interact since I'm not logged in on that URL
Basically, if you're on one instance and click on a link to a post from another instance, it should open that post on your current instance. The desktop version of Lemmy needs this too.
This is really my biggest point of contention with the fediverse atm. Needs to be easier to interact across instances without copying, pasting, editing, or typing in URLs