"Rubato fermata" for more natural playback

Your idea

Add a way to indicate that an individual voice/instrument or the whole ensemble should speed up/slow down momentarily but recover that time a bit later
The icon for it could look like a fermata inside a dashed box like the layout icons
Its properties would be:

• speed change at marker position
• "area of effect" before marker, easing method
• "area of effect" after marker, easing method
• apply effect to voice/staff/instrument/ensemble
• if applies to the whole ensemble: should the time be recovered

Problem to be solved

There is no clean way to get playback that imitates rubato playing intentionally and in a controlled way, which can make solo pieces and lyrical melodies sound "unmusical" as they would be playing 100% in time
Some workarounds for this could be invisible tempo changes and fermatas, or entirely differently notated melodies with complicated rhythms that try to capture that rubato feeling, but I don't think these solutions are always possible and they are never easy to do

Prior art

No response

Additional context

No response

Checklist

• This request follows the guidelines for reporting issues
• I have verified that this feature request has not been logged before, by searching the issue tracker for similar requests

No files, tests, or entry points are named. Start by reviewing the existing invisible-tempo-change and fermata workarounds, then determine how the requested marker, easing areas, scope, and ensemble time recovery fit together. Done would require an agreed design and controlled rubato playback for the listed scopes.