I'm not wholly against the idea either, however it does need some specificity and a very narrowed down range of things that can be done with it. The whole achievement theme that has been going on so far makes me want to vomit a little.
And frankly, as I sit here briefly trying to think of ways such custom titles could be used in ways that you can't already do via how titles currently work, I am strapped to think of any.
Honestly, it more comes down to the fact that if someone is really that worthy of a title, or if you really want to earn someone's loyalty that badly, just find a way to give them a title. And if you aren't really wanting to hand that person much power, yes, there are existing titles to be given out that will not give them much power.