Is it possible to do something like "float:prince-top-or-bottom-if-necessary", allowing Prince to choose whether to float an image out of a 2-column layout to either the top or the bottom of the page?

When using "float:prince-bottom-if-necessary", a figure will sometimes be floated to the bottom of the page and thus moved out of sequence, appearing after a subsequent, smaller image that is displayed inline on the same page. To preserve the sequence of the images, it would be good to have the first image floated to the top of the page instead of the bottom.

Not at the moment, you need to choose to float to the top or bottom of the page.

Do you think it might be feasible (i.e. should I add it as a feature request)?

I'm not quite sure how it would work. Currently you can use float top-if-necessary. When would you want it to move to the bottom of the page instead of the top?