I think the DMs Guild is doing a great job or serving its purpose of:
1) Providing a one-stop shop for D&D PDFs. "D&D Classics" was good, but the name made it awkward as a place for new content.
2) Allowing fans to write content and charge for it.
3) Allowing fans to update campaign settings (over time), rather than having that stuff be hidden away or limited to fan sites and of questionable legality.
4) Providing an avenue for people desiring more crunch and small adventures for their games without requiring them to make it themselves or flooding the market for all players.
5) Allowing the Adventurer's League content to reach a much wider audience who does not have access to a local game store
and allowing those adventures to make money rather than costing WotC money.
6) It's a venue for Print on Demand and selling new hard copies of old books.
Is the Guild perfect? Nope.
But it's easy to forget the alternatives are also imperfect.
Having to find content across blogs and on D&D Wiki? Not fun. And you were never sure of the balance.
Neither was having to learn the OGL and worry about a C&D.
Or the glut of expensive 3rd Party Products at the start of the OGL. Even well known names like Kobold Press or Green Ronin (who can make and sell their own non-SRD games) still have people questioning their quality. People continue to act and think like there's something magic about the WotC logo that makes content more balanced than that of another company's.
Dragon Magazine was nice, but even during it's 4e days (or the Paizo days and the claims of "100% Official!" on the cover) it was never *really* the same as a hardcover book. Playtesting wasn't a thing, and deadlines meant that a lot of "close enough" content made it in.
It's easy to look back at all the awesome stuff of
Dragon, but that's generally ignoring the months of crud that people bought because they had a subscription and no choice. It's condensing months of purchases down to the most memorable content.
And really,
Dragon no longer works. Magazines are a dying industry. Looking at any past issue of
Dragon and so much of it was letters to the editor, editorials, advice articles, copious amounts of ads, fiction, product previews, fluff and lore, and the occasional crunch. So much of that content is no longer needed, as the fluff already exists, the advice is handled by free blogs, letters to the editor are tweets to Mearls, website previews replace the promotion, etc.
From a
writer's perspective it does seem like the Guild peaked. There was the surge of initial interest when everything was new and people were anxious for content. And then it dropped off to a small trickle of sales, for both new products and old. People bought all they wanted, and thus sales have slowed. People willing to use 3PP books bought their fill and are mostly satiated.
Plus, with so much content out there so fast, it's hard to find a gap people
want and are willing to invest money into.
And with so many hits already written, it's harder to get noticed amid the established much-purchase content.
I imagine the future of the Guild will depend on the storylines and if WotC opens up more campaign settings (and which settings). Something like Dark Sun would drive a lot of sales as people update the races, class options, and especially the monsters. Something like Greyhawk... less so. And equally so, storylines that lend themselves to more 3PP support on the Guild would be nice.