Page 1 of 2 of http://www.quickanddirtytips.com/education/grammar/than-i-versus-than-me:
However, a thorn in the side of conjunctionists is the phrase than whom; both sides of the debate agree than who just sounds wrong and recommend than whom in all cases, as in the question "You were faster than whom?"
..."Since avoiding ambiguity awards a point to the conjunctionists"
Google Ngram displays the predominance of than whom until around 1980, when the trend reversed.
How and why does "than who just sounds wrong"? "Since ... conjunctionvists", I prefer than who.
Has than who become (cogently and validly) dignified and usable? Why or why not?