The new Design Ideas feature will surely be useful for a lot of your customers. Unfortunately, as mentioned by a few people in this thread - it goes against our Brand requirements so not something we would want to see in our environment, or at least until we've had plenty of time to fully test it, etc. Definitely needs to be a way to opt in to this, not just pushed out to all customers.
Also, if using the Design Ideas, it would be great to be able to edit an existing page, try out a few of the design ideas, and then Discard the page changes. Unfortunately, as part of the new page co-authoring feature that's currently rolling out, Microsoft are removing Discard Changes for pages. These design ideas are another example of why we absolutely need Discard Changes to stay (as well as destroying our workflows, version history, page lifecycle [draft, published], etc.).
I left a long post on that announcement but thought the need to add one here too so your customers know that Discard Changes will no longer be available (very shortly). There has been zero communication about this change and will cause major impacts for us and across your other customers.