Testflight used to have this Remote Logging feature, even it’s not very stable, log occasionally failed to record, but it’s still better than nothing.
Unfortunately, Apple didn’t keep it after bought TestFlight.
I have played a while BugFender, very great service!
Free registration, download SDK.
Add this line somewhere in marco of your app:
#define NSLog(...) BFLog(__VA_ARGS__)
All existing NSLog will redirect to Bugfender!