I looked and didn't a way to make an experiment specific to a platform. I've noticed that Chrome's about:flags mentions prefs that aren't for the current platform, but they do put them in an "Unavailable" section in this case. I think this is something we could work towards but don't have today.
Bug 1697865 Comment 4 Edit History
Note: The actual edited comment in the bug view page will always show the original commenter’s name and original timestamp.
I looked and didn't see a way to make an experiment specific to a platform. I've noticed that Chrome's about:flags mentions prefs that aren't for the current platform, but they do put them in an "Unavailable" section in this case. I think this is something we could work towards but don't have today.