I always thought Bill's was ripe for collaboration. A brand so hell-bent on maintaining and continuing it's "tradition," collaboration seemed like the easiest and most natural extension into new marketplaces. When you have a company making tremendous pants, why not extend that know-how to hipper brands? Granted, I'm not saying Bill's X CDG, but Bill's could have easily partnered with the younger, "preppier" brands growing up around them. Even though it will likely make Vox's head explode when he reads this, Vineyard Vines comes to mind as a natural collaboration, as do brands like J. Crew (In Good Company), or Club Monaco (who have partnered with older, stuffier suppliers in the past). Even Christian at Ivy Style was all but begging them to do a niche run of high-waisted, slim leg, "Ivy" pants. Just seems like they missed the most obvious, and easiest, play.
The other thing I never understood was why, particularly as they existed in the midst of "Made in America" mania, Bill's wasn't moving to a heavy private label presence. Many "storied brands" are only alive today because of such moves, and because Bill's is far enough off the radar, it would be easy for them to make for RL, or Brooks, or even smaller shops' private labels.
Obviously both scenarios require scalability and flexibility in business, branding and production. However, for a brand that has been cranking for a number of years it's not a stretch to think they could expand their horizons ever so slightly to guarantee themselves another five years of fruitful business.
Nick is right in that it's best to do what you do well. However, when you have the opportunity to (more or less) seamlessly piggy-back off of similar brands emerging and dominating the marketplace, there's no real reason to sit on the bench. Even if it's just limited runs, one season here, one season there, you're remaining relevant and at least putting your name in the mouths of those who would otherwise not even know you exist.