I read somewhere that a shim was being developed to allow reddit apps to join a lemmy instance. Not sure how practical it would be, or how far off it is, but its an interesting idea. Would obviously need to be implemented by the original reddit app dev, or a forked version if open source.
I imagine at least a couple of developers will migrate over here. If they update their app to the fediverse, join in on other open source projects, or just leave the scene is yet to be seen though.