According to Video Games Chronicle, insiders connected to Microsoft stated they were encouraging other studios to stick with a free upgrade system instead of charging current gen customers through DLC. While the Smart Delivery system lets Xbox One gamers bring their titles over to Series X (complete with enhancements), it's only mandatory for Xbox titles.
This also means studios not supporting the Smart Delivery system can still follow a remastered model and make players pay a second time for a game they have. For Microsoft, their message has reached Ubisoft, CD Projekt Red and Bungie - all of which are releasing Assassin's Creed: Valhalla, Cyberpunk 2077 and Destiny 2 for free on the Series X for current gen owners.
VGC also suggested some studios can move around Smart Delivery by releasing cross-gen bundles, which come with two versions of the same game for an increased price. The most notable case is from 2K, who are releasing NBA 2K21 with an optional $100 bundle that comes with the Xbox One and Series X versions. Players can also do the same with the PS4 and PS5 bundle.
The divided support for Smart Delivery isn't stopping Xbox from releasing exclusives like Halo: Infinite with free next-gen upgrades while all of their first party titles will have the system in place. VGC was also told studios without Smart Delivery will lose benefits from Xbox, including cloud saving and cross-generation saving for players.