The biggest problem I’ve had with import/export has been the inability of iOS to correctly save the generated files as .opml from my Links page. Instead it downloads as .php. To change it I have to do a dance of save > move it to a particular folder so Working Copy can see it > rename in Working Copy.
While i understand your frustration at having to allow all text types to fix this bug, it will save me some hoop jumping.
Although, if I could subscribe to/sync with a network-hosted OPML file (automatically adding new subscriptions, etc), that would be even better! π