I find making it an "option" highly pointless.

There are many games out there on steam that have a launcher as default so it is possible.

Pros:

1. People will realize that the game now has a launcher.
2. People will realize they can download mods of the steam workshop.
3. People will realize they can configure which mods can be launched that they have downloaded from the steam workshop
4. People will realize that
5. And most importantly, people that set up their specific configuration through the launcher don't have to keep pressing "Open Launcher" as an option but already have it saved.

Cons:

1. None. Maybe the fact that you have to click 1 more time to get into game?