An IPS staff person can correct me if I'm wrong, but my read of this was not that everything had to be ONLY under uploads, but that it had to be in a single location.
Today, you could have a different storage location for each of the following:
Advertisements, Attachments, Badges, Club Custom Fields, Clubs Images, Custom Emoji, Icons & Logos, Image Proxy Cache, Login Method Icons, Profile Photos, Custom Profile Fields, Social Media Promotion Images, Ranks, Reactions, Referral Banners, Theme Resources, Forum Cards, Forum Icons, Customer-Uploaded Advertisements, Support Request Custom Fields, Purchase Fields, Customer Fields, Payment Gateways, Product Groups, Product Images, CMS Media, CMS Pages, CMS Records, Calendar, Event Cover Photos, Gallery Images
Do we really need a custom storage location for login method icons or custom profile fields, etc?
It SOUNDS like they're saying you'll define a single location for storage (be it the "uploads" folder or an S3 bucket or whatever). Everything would be stored in that location, whatever/wherever it might be. So you could continue to use a CDN, however you would not be able to have multiple subdomains for each of them. It would simply be cdn.domain.com/club_images and cdn.domain.com/attachments or whatever the taxonomy is going to be.