We shipped support for installing the OneDrive app on an SD card, but any files taken offline still go to internal storage. We do have plan to enable offline files to be stored on SD card. I’ll update status as we get further along.Brad Wilson commented
Microsoft, you have got to catch up. We are in a multi-device universe now where our mobile devices are just as important (sometimes moreso) as our desktops and laptops. Your competition is onto this while you seem to be trying very hard, succeeding in places, but missing some very obvious flaws such as this one that results in much of the goodwill you've amassed to be negated. It's a shame.
The general issue that this thread relates to of being unable to meaningfully synchronise files onto expandable storage and then use them offline (just as you can do on a Windows desktop) has been ongoing for YEARS, is one of the most voted requests, is discussed in multiple threads, has had many of your loyal customers literally BEGGING you to resolve it, and yet.... And yet.... You don't even show respect for that loyalty by responding to these threads with even an acknowledgement that you understand the issue.
I'd love to see a senior product manager (not a program manager) participate in these forums and give us a detailed idea about what is in the pipeline. You might be surprised at just how helpful we will all be in giving you a wealth of feedback about how this functionality could best work.