Thanks for the article Stephen. My two cents:
Based on your criteria I don't see how workshop can be unrestricted. It chokes out any other strategy trying to play creatures and the entire metagame is warped around it. When we're at the point where we're restricting cards that are fine in modern we've really gone too far shielding a sacred cow.
That's essentially the position I took a few months ago, and after the NA Vintage Championship. I told Randy before the event, that if Workshop was 5 or more of the Top 8, I don't see how it can justifiably remain unrestricted.
Even before that, I said in one of the SMIP podcast that if the restriction of Thorn didn't do it, then maybe Shop had to go.
But... After watching all of the data since... which shows that Shops are about 30% of the metagame, 25% of Top 8s, and about 55% win percentage... and assuming that holds... I think a more narrowly tailored restriction could achieve the goal of: bringing Workshops Top 8% and overall win % to a more acceptable level.
I think part of my willingness to entertain non-Shop targets is: 1) restricting Shop is a radical act that harms other strategies, and therefore is not necessarily the most narrowly tailored choice, and 2) it's really hard to project what the exact effect of restricting Shop would be.
Let me tackle both separately:
The truth is that deciding what to restrict is a much more complicated subject than most admit or that DCI philosophy and practice acknowledges. The DCI has hardly been consistent in it's policy making. But there is a tendency to hit the 'name' or salient card over a seemingly less powerful card. That makes Workshop or Sphere a much more natural target then Ravager.
Narrow tailoring assumes that there are multiple ways to solve a problem (which is usually true when it comes to B&R policy), and that the means by which you accomplish that end should be that which has the least collateral harms. Therefore, narrow tailoring will often lead to restrictions that seem facially absurd, in the sense that the restriction target is a less seemingly 'powerful' or salient card.
But, there have been times that the DCI has actually taken a more narrowly tailored approach. Remember when they banned Dark Ritual instead of Necro? Trinisphere instead of Workshop?
We discovered that the restriction of Ritual instead of Necro was ultimately wrong, but it was, a priori, the more narrowly tailored choice. Narrow tailoring gives you a higher risk of getting wrong, because there is a greater chance of not doing enough, but it also means that there is a lower overall risk of over-restriction - of restricting too many cards (over breadth - or sweeping too broadly). I consider that a fair trade off. I think the 1999 and 2008 restrictions swept way too far, and were a mistake as a result.
I also think that there are too many instances where restricting the salient card led to the wrong restriction. Restricting Black Vise in 1997 instead of Prosperity, Mana Crypt and/or Mana Vault is an obvious example. Black Vise was simply the win condition abused by having a ridiculous amount of mana to cast Prosperity. That would have been like restricting Tendrils instead of the fast mana or the draw engine. I also regard restricting Gush instead of Mentor is an obvious example of this problem. Gush got too much of the blame for Mentor's behavior, IMO.
Restricting Trinisphere instead of Workshop in 2004 was a very successful restriction, IMO. It allowed three different strains of Workshops to emerge and diversify. It was the right call.
It's possible that no restriction short of Workshop itself can curb Shop deck's dominance. But it's also possible that restricting Workshop itself won't be enough. Take the current Shop Aggro deck, remove 3 Shops, and add 2 City of Traitors, and a Ghost Quarter. Then play Traxos instead of Precurser Golems to bend the curve down even lower. Or Eldrazi Temples and add TKS instead. Either way, that's still a top tier deck, is my guess. It's hard to know. I've been playing alot of Workshops in the last few months, like yourself, and it's not like the old days where you really needed a Shop to explode out.
I'm not theoretically opposed to a Shop restriction, as I've said many times; but it's also possible that you can achieve the same result by a narrower means.