With Patch 2.1, all players now have access to any maps that depend on Heart of the Swarm or Wings of Liberty. This includes both the Arcade and Custom Games.
This means that everyone, including Starter Edition players who have not purchased StarCraft II, can now play any user created map or mod.
Below I will cover some topics that have already come up.
Not only are all maps in the Arcade freely accessible, but all games under the Custom Games section are now free as well.
Note that Custom Games are still filtered by your Expansion Level, so if a map directly depends on Liberty or Swarm Multi it will only appear in the list if you are set to that same expansion level in your gameplay options.
In order to publish a map or mod that depends on Wings of Liberty or Heart of the Swarm, you must still have the appropriate license(s) for those dependencies. This has not changed in 2.1.
I hope this clarifies how dependencies and licenses work in Patch 2.1. If you have any related questions, feel free to ask and I will try to update this post with more details.