The idea is to allow playing with multiple of the libraries at the same time, for comparison, interop or integration. Now, we have a plan to have another module or project for dependencies that are known to slow the build (like kapt dependencies).
We also have the plan to have an Android playground, an iOS playground, and a Multiplatform playground.
We are letting the ideas come regarding the projects organization, as multiplatform currently in alpha suffers from a few tooling issues that we don't want people not trying it to experience.
Once Multiplatform tooling is perfect or near, we will probably make the whole project multiplatform unless unnecessary.