I think what it will mostly do is hardening existing customers anti-cloud stance. There already was big reluctance by many enterprises to switch to Exchange Online and New Outlook due to lack of feature parity and control, to the degree that Exchange Server SE became a product (with support until at least 2035) and Classic Outlook is still the prescribed Outlook variant in many organizations (with support until at least 2029). I also know of some customers, which migrated back from Exchange Online to on-premise Exchange Server because they were so unsatisfied with it.

This will only make it harder for Microsoft to pull all customers to their cloud offerings. I think in general that's a significant blow to SaaS-ification of the field.