The greatest limitation to level loading comes from real-time global illumination. If you remember, when we looked at how it works in Chapter 7, Lighting up the World, we discovered that Realtime GI requires precomputing to work properly at runtime, which cannot be achieved if you are aiming for the procedurally generated level.
A similar issue will be encountered should you choose to add more items to the already existing level. The solution to that would be to bake the lightmap and then deactivate the items you wish to add.
Lastly, there is a modular level generation when you have a set of environments that you are planning to reuse many times to create something like an endless runner type of game. The challenge here is hiding the seams between different modules.