Sideloading doesn’t imply that app isolation (sandboxing) is also going away, nor does it imply that any app would ever be able to trick the user into running i

Sideloading doesn’t imply that app isolation (sandboxing) is also going away, nor does it imply that any app would ever be able to trick the user into running it with escalated privileges (sudo/root) as is the case on most laptops. So this malware that you had to clean off of those laptops would still not be possible, even for sideloaded apps.