My point of view in this cases its "common sense" and dialogue.
In my games I use to advice and delimitate players options. If in a concrete campaign I'm not interested in Force Sensitives, aliens or other things in my game I just tell it to my players and them, nicely, agree and pick another options.
Other reasons could be that, as you said, that the other ones no-FS will get apart. Here are two points: Or tell your player that please, take another option or create a "balanced scene". As I used it before, Naboo battle (or something similar) could be a great sample. Padme fights with Jedis againts B1. Also dialogues and investigates things. R2 repairs and, whit not, maybe can assist in so many ways in battle. BUT, when we arrive at a crucial moment like Duel of Fates, Padme fights and equivalent challenge to her (tons of Athletics/Skullduggery checks and Battle B1 droids) while the two Jedi players fight the Sith guy.
In my actual game I have one nagai martial assassin, a (alien) archeologist/slicer, a FS/Jedi (or something close) explorer and a Force Shaman/Hunter.
In most cases I created scenes where everyone can participate on it in a particular way.
Mechanics, probably will never fight Darth Maul because... is asthetic in SW XD Lightsaber duels rules!
I prefer to dialogue with my players instead change (one of the) SW essence. If Jedi are cool/awesome, then let them be!
Dialogue+Common Sense= Awesome, Fun and almost canonical games!
PS: X from Megaman series is still considered a canon-ical guy? XDDD
Edited by Josep Maria, 20 January 2014 - 05:42 PM.