I've never seen a SaaS product that fits this description. There are always things to do. Libraries to upgrade, performance bottlenecks to diddle around with, an endless stream of nonsense feature requests from people at the customer who never actually use the product, fun experiments your developers want to try out, and so on.
The hard part in SaaS is to delete code, and that's what you should do, at least some of the time. Either through simplifications, or just outright erasing functionality that very few if any of your customers rely on.
What you should not do is let your customers grow the liability that is code in your production environment, unless your entire product set is designed to handle things like this, e.g. the business models of Salesforce and SAP.