I believe this is already supported

see the config entry:

--list of names of valid cover art, must be separated by semicolons with no spaces
--the script is not case specific
--any file with valid names and valid image extensions are loaded
--if set to blank then image files with any name will be loaded
names = "cover;folder;album;front",

and the implementation in isValidCoverart():

if o.names == "" or names[filename] then
    msg.debug('filename valid')
    return true
end

This would accept any image file, the suggestion is to still prefer valid filenames and only fall back to any image if no matching filename is found.

This feature would require some sort of second search of the directory after the first search fails, or alternatively saving all the image files on the first pass and loading them at the end like you did.

However, considering the extra complexity this adds I'm tempted to just say: enable all images and just name your coverart so it appears first. Do you have some use-cases that this feature would solve?