Not exactly what you're looking for, but if I start typing, a list of my existing tags which start with the typed characters pops up (that's in Firefox). I would recommend you use the feedback link at the bottom of lds.org (any page) to suggest adding the list (unless what I describe is what you mean, in which case, let them know what browser you're using so they know it's not working everywhere). It's my understanding that feedback there is more likely to reach the right people than feedback here.
FWIW,
Liz