While talking about the dragon keys a month or so ago, I forgot to mention their other major function in the game.
There will be some doorways throughout the game that you cant open unless you have the propper key to open them. Much like how in most games you have a red key for the red doors, a blue key for the blue doors and so on.
Considering the fact that getting these keys are not really needed to beat the game [unless you want 100% and best ending] I'm still a bit uncertain about how this function will be used. Perhaps gaining one or two of these keys can be essential for completing the game in some way, as you'd need them to access certain key areas.
I'll post more on this as soon as I get some ideas for it. Until then, feel free to post your own ideas/opinions.