At the moment, I'm playing a GSF Conjuration priest whom I imagined using a specific theme for his summons.
However, there's a few problems. First of all, I'm more or less stuck with the current themes until I can find the specific and only one he'd use, which would more than likely require an impossibly high lore skill most character but wizards do not posess. Which more than likely means my Cleric of Stone/Earth is stuck summoning dire rats and beetles.
The second part, these summons are sort of crappy. Even at level 4-5 they hardly last long enough to make a difference, which means we're more or less expected to get up to level 7-9 to actually have a summon that lasts more than a minute or two, even with GSF. As it is right now, I have GSF Conjuration, but I rarely if ever use it in favor of spells of other schools which are about 5x better, even if I've no focus in them.
So I'm making a suggestion. Make Summoning better, a lot of ideas have been made, and a lot of them are decent. I'd like to see themes handled in a different way. I enjoy the research/exploration aspect, but I don't feel it's right for characters of a certain patron summoning creatures that make absolutely no sense, and are unable to help it unless they've got a lore skill of 30 or want to go around gathering obscure and unexpected reagents when the most obvious ones don't even work.
I think GSF should allow a second or third summon and the duration should be kept. I further think that the themes/race of the character should have some bearing on what they can summon.