I'm A Banana
Potassium-Rich
That depends. I know we have a lot of people here who buy everything that WotC puts out for 5E, but is that a representative sample?
If the majority of D&D buyers buy all of the stuff and want things that hew toward a Forgotten Realms-ish vibe, then yes, experimentation would probably hurt sales.
On the other hand, if the majority of D&D customers actually don't do that, and WotC is currently mostly catering to a plurality that likes its current offerings, then trying new things to sell to those other people are worthwhile.
I think it's worth noting that the $1 million Kickstarter club has plenty of 5E material on it, and very little of it looks like what WotC produces in-house. The question is how well that would sell compared to, say, "Hey, kids, let's adventure a week's journey away from Waterdeep" campaign #14.
I actually see it as quite the opposite.
The majority of D&D players don't buy all the stuff. They buy the core rules and maybe some big supplements that clearly fit (maybe they support popular archetypes that aren't common enough to be core, for instance).
Experimentation doesn't produce new sales much in D&D because experimental supplements (like 3e's Magic of Incarnum or 4e's Hammerfast) don't have an automatic home in a lot of campaigns. They're not part of the games that people are already running. Their games don't need the new experimental thing. Rather, their games need rules for things that are already expected in their games.
The $1 million Kickstarter club for 5e includes a lot of low-hanging fruit. Dungeons of Drakkenheim is a Dark Fantasy setting. Flee, Mortals! and Heliana's Guide are variant Monster Manuals. Strongholds & Followers is a supplement for a thing D&D heroes often do. They are very well done, but I wouldn't call them exactly "experimental." Heck, there's a good segment of "bringing back the past" in things like Strongholds & Followers and Flee, Mortals!
Which is why these can count as "big supplements." They're playing in WotC's blind spots, supporting things that people have in their games already (monsters, PC strongholds, dark fantasy vibes, etc.) that WotC can't or won't make, but they're not doing much that's actually risking alienation or asking audiences to accept something new.
I think experimentation is something that is a big risk under a purchase model. A product for purchase needs to convince you that it's worth it to purchase (and most experiments won't do that). Under a subscription model, where everyone is contractually obligated to give you $10 this month regardless of what you do, it makes more sense.