The editing information is small – that’s not what causes the issues with memory. It’s the sheer amount of memory that RAW images consume when they are decoded.
The key difference between iOS and desktop operating systems is that iOS has an absolute memory limit (which is the amount of physical memory in the device). On iOS, if an app allocates more memory than is currently available, iOS will often kill the application (force it to crash). On Mac and Windows, an application can allocate more than is available and the operating system can adapt to it – far beyond the physical memory of the machine. On iOS, if you are applying presets in the background + you are editing, then that’s two full size RAW images. A lot of devices simply don’t have enough memory to load and process two images (much of the memory on a device is allocated to the operating system – apps don’t get access to all of the RAM.)
To your other point, ratings and flags are is coming in RAW Power 3.0 as well (it’s a big release, which is why it’s taking a while to implement). The Mac version will have all the same features as well.