I love the idea but I'm unsure how I'd save a profile theme and allow you / others to switch between them without potentially losing content that is not theme related.

For example, looking at your profile page, I imagine you'd want to change the flowers on widget titles & spoiler titles as well as the images that define your profile look / feel. However, I can only save full snapshots of the entire contents of each custom post / about widget, not parts of it.

So, let's say you "save your profile" as "Original Kitt-Chan". You then change the titles, themed images and profile banner to be "halloween themed" for the 1st of October. You save this one as a "Halloween Theme". During the month, you tweak your about me, add another stamp, update your trade and collabs and get a new fanskin. When November comes you want to switch back to your original theme, so you resave the Halloween one, load the "Original Kitt-Chan" and it not only looks like your original profile theme, it IS your original profile... you lose all changes to your profile, not just the theme changes. I don't know how I'd save only theme related changes.

I've also thought about saving widget layout & sizes because that would be easy but that has limited usefulness without also saving the contents which has the issue(s) described above.