I'd be down for this. There needs to be a broader range of optional content, and there especially needs to be a bigger variety of challenging content. There's basically no gradation from faceroll to Coil/Extremes (and some of the Extremes are pretty faceroll).
And yeah, plenty of people won't run them much without some kind of reward. So give 'em some run-X-times achievements, some exclusive vanity gear, maybe some kind of unique currency with rewards behind it.
Don't make them just another way to grind Tomes of the Moment. It'll either be efficient, and tons of people who don't actually enjoy them will run them because they feel like they "have" to, or it'll be inefficient, and people who would otherwise run them won't, because tomes are hard to ignore and time is limited.