http://www.ncbi.nlm.nih.gov/pubmed/24773771
"This would suggest that there may be a continuum of minoxidil response directly proportional to sulfotransferase activity in the hair follicle. Extending this logic, this finding implies that upregulation of sulfotransferase could potentially be an effective adjunctive therapy to topical minoxidil. Many compounds have been reported to upregulate sulfotransferases in the liver (13,14). We are now investigating the effect of novel compounds on sulfotransferase activity in the scalp."
I guess upregulating sulfotransferase can induce a response to non-responders and can enhance the response to people who do respond. But there would obviously still be variability in effectiveness between people even if everyone hypothetically had 100% sulfotransferase "activity".