I am an avid tech enthusiast. I think that lemmy as a project won't outright kill/replace reddit ever, rather the influx of enough users will eventually build it into a platform of is own. Reddit might still exist down the road, some parts of it might even thrive, but lemmy is, as someone else put it : the first time in a very long time something new in the internet to get excited about.
I think in the immediate future the priority should be to bring more features to it, develope it into a robust ecosystem with all the necessary tools required. Currently it's all janky and cumbersome to use, but the more tech focused crowd is putting up with it because we all are either excited by something new or we just lost our trust in reddit.
I think a short time down the road, there will be a lot of features that we cannot currently imagine. There's speculation that users and even communities will be able to migrate. Currently it's very difficult to find large communities on a topic so information is very fragmented. It's also not too easy to find and subscribe to them.
But essentially, my hope is that development is fast enough, and that new user influx is large enough, that in few months to years time it will be possible for me to host an instance on my own pc/laptop. There I can make my own account or perhaps the accounts of my family/friends so that it always stays with me. I would then be able to bring all the communities under that umbrella.
As for larger communities, I think eventually we'll end up donating to a pool for every particular community that we like. Maybe even organizations can bring their instances as well. And it would still work because no one has absolute control over everyone