I posted visualizations for a pretty similar idea here:https://forum.renoise.com/t/brainstorming-audio-tracks/24794
I don’t think lengths for each track should vary… it would be a visual communication nightmare and require a major change to how Renoise currently functions. What I propose in the link above is a new system for arrangement and composition. It is verrrry similar to the ‘song tab’ idea, except I think it’s not as hodge podge (I think just mashing entire song’s together is inelegant). In short, the post above outlines a system for higher level tracks called “layers”. Layer’s contain a series of patterns + tracks, just as we know them. Operating in a new layer offers the opportunity to create a new series of patterns/tracks (with lengths and effects separate from other layers) which can be arranged to run alongside sequences from other layers in the arranger/composer view. All samples would pull from the same sample pool, so not much else in the program would need to change. I also don’t think the bpm should differ between layers, but that is certainly debate worthy.
I’ve been working more on visualizations for this proposition… will post an update soon.