Christian, thanks for a response! This makes more sense now. Yes, the cloud version obviously will have some limited functionality, it's understandable. But I really doubt we'll be going that way any time soon.
We're already trying to cut down on BDC, but sometimes there is just no other option. It looks like if we ever switch to S/4HANA then at least we won't loose all those interfaces immediately. Although if by the time it happens SAP somehow covers everything with OData services then it'd be load of work to convert everything. (Well, that's probably the least of our worries at that point.) 
Thanks for the replies, everyone!