Allow other rhythms than daily.
I like to memorise twice a day, and it would be great to be able to mark a card as "maybe known till the evening" - no longer having it appear in the morning, but seeing it again in the evening.
Other people may have still other work rhythms (say, every other day), so having this as a general feature would be nice.
I take siestas, so I do sleep between the morning and the evening session.
The problem with grading something as a 2 only when I'm ready presumes that I can predict when I'll forget a word. In reality I have no idea how well i know something unless i'm forced to go back to it a half hour or a few hours.
You're absolutely right, mnemosyne inherently covers the seconds to minutes time scale. However, it is entirely lacking on the scale of 25 minutes to 5 hours (to use Pimsleur's system as an example again). If i were to take me anywhere between more than a few minutes and a full day to forget a word, then 1 day is too long of an interval. This isn't an obscure case, either; a significant portion of my words fall into this category.
Note that the definition of grading a card 2 or higher is that you think you will remember it the next day. If it turns out you forgot these over a span of a few minutes, you probably graded it 2 too soon :-)
Also note the importance of sleep in memory consolidation, which is the main reason behind SM2's focus on daily scheduling.
I don't know if it's because I learn 50-60 cards per day, but many of these I will forget by the time they come back around in a session. this is over the span of a few minutes; A day is far too long for a word i just learned!
Pimsleur's system consists of intervals of 5 seconds, 25 seconds, 2 minutes, 10 minutes, 1 hour, 5 hours, 1 day, etc. making a pimsleur plugin that transitions to the traditional algorithm once you get to 1 day would be perfect!
A very simple step towards this would be to allow a manual transition to the next session instead of the automatic timed one. I could then manually transit before each session, more or less than once a day as convenient.
Ideally there should be a calendar interface, where the general rhythm can be entered (e.g. twice daily on Mondays, Wednesdays and Fridays), and where individual deviations can be indicated (next Monday I won't have time to review, but that Thursday I'll be available).
I realise that would be a major feature, but it would be a very nice one.