still +1 for “reversed autoseek”
^Thank you for bumping this. This feature would be incredibly useful.
Pretty old topic 
It’s a simple idea, but probably very difficult to implement.
If it was to work flawlessly (considering glides/portamendos et c into calculation when they ocurr before the note), this feature seems to have almost the same technical complexity as the good old request of pre-rendering a perfect waveform display.
As also suggested before, perhaps a comparatively ‘cheap’ feature would be enough, just helping the user to place a single note in a one-shot process (only affecting pattern data and not being a feature of the actual instrument). The drawback here seems to be the non-predictable effects it will have in regard to pattern boundaries and a pattern sequence with repeating/non-sequential patterns. “Magical notes” would always be consistent and predictable in that regard.
A third option, that might be the simplest in terms of dev practicality (?) but also the most limited, would be to extend the track delay to allow much more than ±100ms (or a separate track delay parameter if that’s suits the ‘internals of Renoise’ better). This in conjuction with good time displays in the sample editor would give the user a fairly quick way of aligning a whole track, at least. Drawbacks are obvious - i e not an instrument feature and would require a whole track for taking care of just one sample/pitch.
Even though the note align feature would be very useful and cool, I would fully agree with devs if they say it takes too much time to implement.
+1 for cheap version, don’t over complicate things and scare devs away 
Can’t this be scripted though using one slice marker in a sample? If you know the song’s bpm/lpb/(sample rate?) details & amount of beats/distance between the start of the sample and first encountered slice marker, it should be possible to determine the amount of lines back from the cursor in the pattern editor a sample should be placed?
I put a plus one into this one, too.
I think it could not only be useful for “whiplash” type sounds, but also for aligning transients of percussive samples.