It is 100% what will happen in the future for tons of reasons. It makes more sense as people download things to have access to them at a later time. The cloud is the cloud, independent of physical devices which do get lost and will not always continue to work. + Cloud storage has become a commodity.
Why isn't cloud download as default already happening? Sure, not everyone buys enough cloud space to have downloads be to the cloud by default, but it should probably already be an option in browsers/devices since lots of people do. Why isn't it?
I think the answer is that some of the browsers actually care about how their users use them and don't want to add extra clicks.
That said, being able to specify a default location seems fine. I thought I could already do this in firefox, so of you want to, just setup the default so it saves to your cloud provider
Microsoft pushed OneDrive heavily when it first came out. They made it the default for Microsoft Office to save documents there, but frequently OneDrive was broken and when that happened π° πͺπΆπΌπ³π«π΅'π» πΊπ¨π½π¬ π«πΆπͺπΌπ΄π¬π΅π»πΊ π¨π» π¨π³π³!
Guess how many times I've used OneDrive since?
To save something means to have it locally available, not copied from one third party to another.
Can I recommend you turn the Internet off for a few hours and see how your life goes? A week without it should be a dream, not a nightmare.