Would it be possible to have graves disappear after X seconds (say, 300, 5 minutes by default). After which, the items will be released as they would a regular death.

I like the idea of grave expiration, but think it should be disabled by default. A longer timeframe would probably be appropriate, as well. Perhaps 10 minutes and then it automatically dumps onto the ground but only has one minute remaining on the entity deletion timer. Alternatively, you might try ensuring that the owner of the grave is able to access it? I would either use a fake player or I would work around the typical block interaction permissions and just check that it's the grave owner before allowing access.

I somehow understand this one. When you have lots of players (especially on open servers), spawn areas (and other protected regions) might get messy. I recently fixed that (39b3e23, though I'm not sure if it works with plugins), but graves expiration may still be option for larger servers (since it's still reduces entity count and allows extending drops below vanilla 5 minutes)

Though if I'm adding this one, it's never going to enabled by default. It will be config option, and it will be up to server admins to deal with all that grief and discontent it causes when enabled.

Well, the main issue is graves getting stuck in someone elses land, but if your checker is in a stable enough build I can try that out. What happens if a grave can't be placed?

Probably nothing production-ready. And I'm generally against using snapshots on larger scale.