Well sure you shouldn't rely on anything new for core aspects of your application without a plan for what happens if they go away. Especially when the API in question isn't even implemented yet...
But that's not how I understood your comment above, which was to not rely on any browser features for native access, which IMO isn't good advice.
Sure, you shouldn't go out and build a business around the "Web Writable Files API" tomorrow, but if it gets standardized, and if it gets implemented in a few major browser engines (which is a requirement for standardization in this context), then yeah go ahead and start to rely on it more.
But this has very little to do with these new proposed APIs, and more with general software development.
But that's not how I understood your comment above, which was to not rely on any browser features for native access, which IMO isn't good advice.
Sure, you shouldn't go out and build a business around the "Web Writable Files API" tomorrow, but if it gets standardized, and if it gets implemented in a few major browser engines (which is a requirement for standardization in this context), then yeah go ahead and start to rely on it more.
But this has very little to do with these new proposed APIs, and more with general software development.