The way i see it, there is many different things you can do with it, because.... Although I am not 100% sure it does, ludins echo will proc the thunderlords yes? it is damage because of an ability, because an ability is needed to be cast for the item to work, and so i believe it is set to proc the thunderlords..... but anyways, twisted fate doesnt need to be able to proc thunderlords in all honesty, if done right you could proc lichbane, thunderlords, ludins echo, his Pick a card, and his Stacked deck, all in one auto attack.... that is a rediculous amount of damage even without the thunderlord's proc and with next to minimal effort.
As to the others being super niche, yes that is true, it really is super niche, but taking out the thunderlord's auto attack wouldnt make it any less (for the most part) generic, because most champions who do not have 3 damaging abilities, either shield/heal, or they do enough burst damage that they could make use of stormraider's surge, there is very few champions that could not be classified into that, that i can think of at least.
As to it being the only offensive keystone in the tree, stormraiders could be in theory considered offencive, but you do know that Cunning tree is made to be more for utility? you can do 12 points into it and easily get almost as much out of it still. Along with that, but most burst champions have 3 damaging abilities, or else they do not burst quite as well as others.
I do agree with you very much Nameless Voice, the damage over time and auto attacks i feel could refresh the time it would take to proc the thunderlords, kinda like with velkoz's passive, just much shorter timeframe, but adding an additional stack per each tick of damage over time is kinda excessive.... same with auto attacks in my opinion as well, it will add a little more skill without it being completely nerfed.... just takes a bit more commitment to do.