Your light side ending seems very neutral to me, beside in my opinion light SI would put benefit as second if not first priority.
There are two possibilities there (only talking about light side).
It will either be an operation which is team up all the heroes (may be even from both sides) and several npc to fight Emperor.
If it is a solo mission, then It would be big boost on the power level or make a sacrifice , or both since you are going to fight such powerful being. SI wont fight alone certainly, there will be Revan and few others. The option around Darth Imperius should be focus on maintain the power of the Empire not personal. You can still bind Revan as a light side choice if Revan agree to do that. But that will leave a problem to other class since they don't have that kind of ability. And I believe if Bioware allow you to do that, there will be a big cost on doing so as your body may not be able to with hold such power. It could be a light side choice which SI need to make a desperate move to save the Empire and he/she decide to make a self-sacrifice making his/her body as vessel to hold great power in order to defeat the Emperor. It could make very dangerous at that time and might get killed, but in the end SI could still manage to survive somehow.
My idea right now is, since my SI is completely light sided, at the beginning Empire and Republic try fight Emperor by their own. And got defeated or at least mess up. The Emporer's force is too powerful and eventually sacrificed a world to regain his physical form somewhere during the story. The first part of the story, SI possibility run though different planets to regroup the remaining forces and stable the defense line. Then the Emperor make his return and SI and many others believe they cannot fight alone. And SI need to persuade others to make another alliance with the Republic. There will be some in-fight and conversations , and may be kill some sith in process, and meet some Republic guy in the end (Theron should be one of them). And then SI take the fight to the hands and Imperial Guards. Though FP and OP SI barely beat them. SI believes they cannot beat the Emperor with the power they have right now. So SI need to decide how he/she get the power. It will either be a dark side choice which will involve killing and sacrifice other people, or a light side choice. May be involve searching knowledge and so on. After that, SI need to get a device which could destroy the Emperor completely. And then with help from Revan , SI face the Emperor. Then upon using the device here comes a problem which may involve sacrifice on the user. My SI will decide to do it without sacrificing other people, and kill the Emperor. SI thinks he/she would go down with him, but survived somehow.