Either way Fcp doesn't know where you want the data to go uness you tell it. Do you mean if setting the scratchdisk was added to the "easy setup" window or if it would be added to the "new sequence preset" window when selecting a new sequence? I can see this being valuable saving time but dont know how Apple could pull it. Whatever that means... I need to think about it now because i love that idea also wondering why it has just now come up, or has it not?
I've been requesting this from Apple for years. I don't know why they have not done it. I jump through 4 projects a day so I really need it. I don't know of any shortcut ways though.
Larry Jordan, who writes a great monthly FCP tips letter (larryjordan.biz) says this about it:
Have one main "FCP files" folder. Assign the waveform cache, thumbnail cache, and autosave vault to this folder. Change only the scratch disk selection to the project you are working on. This is because the three cache folders hold an insignificant amount of files (small in terms of size). Also, each time you create a new project, FCP will create a new folder in this "FCP files" folder with the project name on it. That way, it can be easily cleaned up after a few months work.
I do not remember what newsletter number this was from, but I can look around for it. In reality, I don't even use this method because I am very particular (ie: anal) about where all files are at once.