I think the other missing pieces I've found are upscaling and stem splitting. While existing tool exist for splitting stems exist, my testing found that this didn't work well in practice (at least on Suno music), likely due to a combination of encoder-specific artifacts and the overall low sound quality. Existing upscaling approaches also faced similar issues.

My naive guess is that these are things that will benefit from being closely intertwined with the generation process. Eg when splitting up stems, you can use the diffusion model(s) to help jointly converge individual stems into reasonable standalone tracks.

I'm excited about the potential of these tools. I've definitely personally found uses cases for small independent game projects where a paying for musicians is far out of budget, and the style of music is not one I can execute on my own. But I'm not willing to sacrifice on quality of results to do so.

That's their "Remix" feature which just got renamed "Reuse prompt" or something.

Their extend feature generates a new song starting from an arbitrary timestamp, with a new prompt. It doesn't always work for drastic style changes and it can be a bit repetitive with some songs but it doesn't completely reroll the entire song.

We just published a blog today discussing this - https://montyanderson.net/writing/synthesis

Variation in small details is fine, but you need control over larger scale structure.

At some point it's just not efficient to try and get the desired output purely through a prompt, and it would be helpful to download the output in a format you can plug into your DAW to tweak.