What are the limitations of aquafaba as an egg white substitute?
I don't think it is useful to think of aquafaba as a egg-white substitute. Rather, you should think of whipped aquafaba as a replacement for French meringue, in cases you are not relying on it setting under heat.
So, when you need a vegan foam, you can try aquafaba (after whipping) to get the right texture. To regard it as a general replacement for egg whites is an exaggeration.