The idea is you can subscribe and interact with any instances, no matter what instance you came from

Sure, most will jump the bandwagon into lemmy.world.. at least for the near future. I can say that with confidence because when you search "how to join Lemmy", most guide will point you to Lemmy.world instead of.. lets say.. coughLemmynsfwcough

Over time, some will eventually move to other instance (mostly just the account, because they want 'cool username' for themselves). Sooner or later, things will balance themselves out.

Maybe you can even start by deploying your own instance, for no other reason than claiming your own 'cool username'.