Right now lines (particularly those with effects, such as hairpins and pedal lines) only tether to existing beat divisions in a score. This makes sense, of course: more often than not it makes no sense to have a hairpin or pedal line not particularly tied to the start or end of a note. However, there are a few cases that I've encountered where this behavior doesn't quite add up, particularly regarding playback.
1) I've encountered a few scores now where the piano pedal indications do not quite work with this system. Specifically, de Falla's Fantasia Baetica requires, at one point, to pedal specifically on the playing of a principal note such that the grace note is not pedaled.
2) For instruments that can crescendo and decrescendo freely (wind instruments, stringed instruments, etc.), particularly when they are in a work that includes other instruments such as orchestral works, their hairpins oftentimes apply to a sustained note in the middle of a measure.
Now, this behavior can already be to some extent accomplished by placing invisible rests in a measure in some unused voice. This works, but oftentimes screws with measure spacing.
Hence, the feature request is an option, for a given line object, to mark it as "freely anchored". A line object marked as such will then anchor freely to (16th/32nd/64th, something configurable in a setting file or something) beats in a measure regardless of whether or not there's any actual note object at that beat.
I know, here I am making yet another suggestion that only really alters playback, and one with an already-existing workaround even. Still, figured I'd at least suggest it.