I don't think it will be as much of a big deal as people think. Before the major aggregate sites, there's been web forums. Nobody had a problem with it, even novices users.
Second, it's not like it wasn't happening on Reddit anyway. For example there was r/askscience and r/sciencediscussion. Splinter subreddits were very common, and you might want to sub to 3 or 4 to keep up just with one topic.
It may actually be a good thing, because similar looking places may have a different feel/scope.
I mean, on Lemmy you can also specify a display name, i.e. a short description right on the home screen.
Finally, it tends sort itself on its own. I've already seen one example where 4 communities with the same name popped op, and after one ran away with popularity, another one shut down and the last two just link to the now "main" one. I suspect it will often be the case that just one or a small handful will grow to be major, and the rest will wither off.
Let's wait a bit, these are just the super early days remember.