I tried modding in a race that doesn't have (or need) a Homeworld, by using the Pirate Faction as a starting point. So I added the tags to my custom race
<RequiresHomeworld>false</RequiresHomeworld>
<HomeStarSystem>InvalidDef</HomeStarSystem>
Just like it is on the Pirate faction Defs.
The race does show up on the list, and the "Homeworld" field is empty. However, when I try to start the game, it'll say "Building Map" for a few seconds, and then instantly crash to desktop. No crash log or dump is generated (is that because we're out of Beta? Is there a way for me to force it to generate those?).
I understand that I might be pushing against the modding limitations, but where's the fun in conforming? 
As a sidenote, and slightly related to my project: Is there a way to allow shipyards to stay orphaned, regardless of if we have enough planets to sponsor them all?