Support extended OPML data from other outliners

I'm looking for a replacement for my current outliner, Circus Ponies Notebook, which was very popular on the Mac. But the company closed and the app no longer runs on the current macOS. I can export my files into OPML that can be pasted into Workflowy. However, the OPML contains extended data that isn't imported, but does correspond to features in Workflowy, like status checkboxes, creation* and modification dates, etc. I'd love it if Workflowy could also import this data! An example:

<outline text="this line has a checkbox and is marked as 
completed, and a keyword of &quot;office&quot;" 
category="office" _status="checked" created="Sat, 29 Jun 2019 21:28:49 
GMT+2" changed="Sat, 29 Jun 2019 21:28:53 GMT+2" completed="Sat, 29 Jun 
2019 21:28:53 GMT+2"/>

Extra fields like this, e.g. the _status, are also supported by some other outliners. I can send more information if you're interested...

*display of creation dates would need support in Workflowy, I think this is already planned, see https://workflowy.zendesk.com/hc/en-us/community/posts/360077942772-Creation-or-alteration-date