Can every companion eventually get all talents maxed that are available to them? (I am not talking about epics)
Sort of, in stages. In stage one each talent maxes out at 4 each. Then when they get to a higher level it recycles and you can add another few of each thing. So you can max out for a bit then more are added so you can continue to boost your favorite things.
I haven't seen it happen yet on any of my own companions. I've got companions who are levels 65-67 and they get SOOOO close to being able to choose all the talents but no such luck yet. The companions I have gotten closest with are the ones who are that high of level and have gotten 3 promotions. Usually, I am still left with 3 Talents not being used by the time I get done selecting their New Talents.
I can't even say with any certainty that this would happen with future level increases because right now I'm able to go up to picking the same talent (Accuracy, Rough, Armored, etc) four times. Which means that if their levels get raised, I am going to guess that we would be able to increase some of those up to 5 or even 6 times. So, again, I think it highly doubtful that we'll be able to pick ALL the talents the x number of times.