As long as its modest and culturally acceptable as modest (I heard that some cultures consider showing any part of the leg to be immodest), that's all the requirement "needed", IMO.
That said, if someone walks into church with a miniskirt and a really low neck line, I'd hope that you wouldn't shun her over it.
If she's an established member and a sister in Christ, then yeah the pastor should talk to her about it. But if its someone new, doing that would likely run her off.
/ captain obvious
Reading the article, it specifically mentions that these are "so-called "mature believers," not lost souls or baby Christians—"
In which case, this isn't a matter of dress during the church assemblies... It's a matter of lack of understanding or out and out rebellion on the part of these sisters. I agree with what King James said about being your church self all the time. Sure, perhaps when going to church one might up the formality of the clothing (in Idaho, this means wearing your dark wash jeans and shining your cowboy boots), but nonetheless the modesty aspect should be in place all the time.
It's not OK to dress like a hooker in church... and it's not OK to dress like one when not in church either.
The fact that this is even being discussed is part of a greater problem among Christians of being kind of "in your face" about "rights" rather than adhering to Philippians 2:3.
As to head coverings, I think we have a tendency to err when thinking of what "modest" means... We've kind of twisted it to mean anything not sexual... In reality it means dressed proper to the occasion and in good taste.
I was in town yesterday doing my shopping and at the store there was a family. Younger couple, 5 very adorable kids. The man wore a long beard, long-sleeved shirt, suspenders and a type of pants that was not jeans... the three sons wore the same type of shirt, suspenders and jeans. The wife wore an almost floor length, long sleeved dress with a head covering and the two daughters wore the same...
STOOD OUT LIKE A SORE THUMB IN 100+ DEGREE WEATHER IN WESTERN IDAHO IN 2013.
Seriously, everything about the way the people were dressed (and I want to be certain everybody understands I am ONLY speaking of the way they were dressed, not their behavior) just seemed to scream:
LOOK AT HOW HOLY WE ARE... WE ARE SOOOOO MUCH MORE HOLY THAN ALL THESE PEOPLE IN SHORTS AND T-SHIRTS!!!!!
Now I'm not even going to begin to judge these people for this. I'm fairly certain they were either Amish or Mennonite or of a similar denomination and were simply following what they have been taught that they should do...
I'm just pointing out that this isn't what the Bible speaks of when speaking of dressing modestly. As Paul instructs in 1 Timothy 2:9-10 "Likewise, I want women to adorn themselves with proper clothing, modestly and discreetly, not with braided hair and gold or pearls or costly garments, 10 but rather by means of good works, as is proper for women making a claim to godliness."
We should be dress properly and noted for our deeds, not our clothing. If the clothing causes the individual to stand out like a sore thumb in one's society... then it's really not proper clothing. This is true if it's calling attention because of being overtly sexual, ostentatiously rich, or archaically "holy".