A feature request:

Would it be possible to add a filter for m+ dungeons, which displays only the keys that can improve our score (i.e. keys higher than our highest timed run for given dungeon)?

It would probably be possible by using C_PlayerInfo.GetPlayerMythicPlusRatingSummary("player") and C_MythicPlus.GetSeasonBestAffixScoreInfoForMap(mapId) but looks rather complicated. Since you have to complete a key on both Tyrannical and Fortified, it can get a bit tricky to find out if you can improve your score this week in a specific dungeon. Wowhead has a guide on the rating system. I will keep this issue in mind and would appreciate a PR.

Is this possible without reading the protected name string to find the key level?

You are right, reading the key level is not possible, making this feature pretty much impossible. I should have thought more about the requirements.