A bit much?
Although there should be at least a silver trophy/25G for each specific one we manage to kill.
Specific, scripted ones within the main questline I could see this happening with, but it's been confirmed that there will be random, unscripted dragons, as well. Too many dragon-achievements, and you risk watering down the prestige of it all, but if there are only a few of these within the main questline, it will have more meaning to the player for having earned them.
I suspect there'll at least be a "Killed Your First Dragon"-type trophy in there somewhere for your initial cherry-popper kill, similar to the "Closed Your First Oblivion Gate" award.