I think what apple will do is kill macOS and MacBook lineup entirely and replace macOS with iPadOS. Adding mouse support while maintaining touch support is one step towards that direction. iOS 13.4 mouse support works surprisingly well, to a point that a standard two-button mouse can complete almost all iOS system-wide activities. With catalyst introduction and macOS running iPadOS app, what’s left for macOS is full access of the file system, terminal, a bit of UNIX stuff and a bit better versatility for most people. So, instead of trying to open iOS file system to the end user, Apple instead will kill macOS in favour of locked down ecosystem.And because Apple has doggedly protected the iOS ethos, there will never be a time when iPads properly replace Macbooks. That would require Apple to put a door in the walled garden of their ecosystem and open up the filesystem to dispense with sandboxing and make it universally accessible by apps.
Just a while ago, Microsoft released their windows 10X preview version for those “dual screen” devices. It looks ok, control is a bit messy at this stage and the system’s response to traditional Win32 application is a bit unpredictable. However, one takeaway is this version of Windows 10 locks users access to system files more and more. Default file explorer hides system folder, program folder and windows folder from users completely and there’s no option to display those folders. If Microsoft can attempt to lock their system down in this future version of Windows 10, I don't see apple not doing the same.
In short, I believe given a couple years, Apple will kill macOS and MacBook lineup entirely, and completely transition to full mobile device era with iPad and iPhone as the hub of the entire ecosystem. More and more devs will port their old macOS application to iPadOS when possible, and iPad will be the laptop we used today.