I think part of the difficulty is you would still need a text file that contained the name of each function.
Then the system could pull/check the list with text prediction. It wouldn't be much unlike how your doing it now. You would have to maintain the list of function names yourself and then have functions to check against that list.
What would be cool is if when you create a uniquely named function, the system automatically added it to an internal custom list for later access. Then it's baked in. I'm not sure of the performance demand on this though.
There might be a way to build a plugin for this, but I've never played around with the SDK. Any update on if anyone is working on something like this or maybe the devs?