There are a lot of missing affixed form compared with the old MySpell dictionary in the new Hunspell en_US, for example missing YS flags of abdominal (eg. "abdominally" is not recognized now). I believe, we need to limit only rare root words, not rare affixed forms (especially for long roots, those couldn't be confused).
The future will be a full morphological description of the English dictionary removing the not special affixed forms from the dic file and optionally add morphological descriptions/stems etc. for Hunspell.