I would like to see darkside characters approach the force in a different way than non-darkside characters. It is often represented in the EU fiction and even in the movies that this is one of many ways that sith approach force use as opposed to the Jedi.
As such, I proposed that when a character becomes a dark side character, the instead of using discipline to activate force powers they would use coercion. This would accomplish a couple things that I would like to see represented.
First, it would make becoming dark side have an additional consequence, showing that the fundamental approach to using the force changes, not just that you want a different colored pip. Intimidation and fear becomes the character's modus operandi, and creates a different synergy.
Second, it reinforces the mystique of the sith and other darksiders and how they are "unnatural" forcing and coercing the universe to bend to their whims and not living in harmony with the force. This is mostly a fluff/lore element, but would do a lot to help play up a character's fall. Suddenly their inner peace is not attainable to use the force in the same way.
Lastly, this would create an interesting penalty for going darkside. dumping all the xp into discipline is not a one size fits all solution. it helps characters that would tread the line from just going darkside without hesitation as they may not be as successful at their force powers. and once a darksider has embraced the coercion use if they are redeemed, they have to change their approach at force use again.
I feel this would enhance some of the consequences of going darkside and being redeemed, and would help differentiate character design.