Ancestry - please tread carefully. This request (formatting text data) has the potential to seriously impact tree exports to GEDCOM files. The GEDCOM standard doesn’t provide for formatted text and the current Ancestry implementation of “Descriptions” works with some desktop programs but is already sailing dangerously close to the wind even without the overhead of text formatting.
It would not be acceptable for an implementation of text formatting to simply stop all exporting of formatted notes and/or “Descriptions” to GEDCOMs.
If proceeding with an implementation of formatted text please, please, pretty please – thoroughly test GEDCOM export and re-import. Test imports back into a member tree and also into popular desktop programs (and not just FTM). Sadly Ancestry has a history of broken GEDCOM export files.