So I've been tossing this one around in the old noodle, and thought I'd put it out there for you to shoot down: Audio-only Core 6k.

That's right, completely ignore the Japanese text. Listen to the audio as the question, and grade yourself based on understanding the sentence (this could be pretty subjective of course). You would need to see the English translation the first time for each card, but that would pretty much be it as far as text is concerned.

As someone more interested in listening/speaking than reading/writing, this appeals to me greatly (at least for the early post-RtK phase). Has anyone tried this?

My core deck has both directions for audio/kanji and kanji/audio.
I found that doing kanij/audio only was much harder than doing both, such that despite having twice as many cards to review, it was often easier.

The problem I had and maybe others may have is that without writing out the vocab parts, a word you hear is usually all or nothing. I found it much easier to both guess new words and get hard to remember words when the -yomi is known, and you wont likely get that with sentences alone.

Hmm... I've been doing something like that...

When I complete a list, I import it into anki. My flashcards all have the audio on the question side with the japanese on the answer. This deck is seperate from my sentence and vocab decks.

I like it because its a relaxing review session. I lean back, eyes closed, just slapping the space bar.

Sounds pretty good. Kanji gives you clues you don't have in speech, so I think it's good to go without. I would do of the individual vocab words too tho as I'd want to recognise the word outside of the sentence too.

Used to do it (over a year at least), but it does take up time. I stopped doing it earlier this year on the idea my listening "test" would be from subs2srs so my vocabulary is now just the word in a really big font with the sentence in a smaller font (counts as 'hard' if I have to read the sentence to get the meaning).

Yes, it's a good idea, but be willing to move away from it after time if you think your listening is being tested by other means.