If I'm not wrong MXP files are just zip files with a configuration file inside. Well if you're using Flex then MXPs will be useless due to the fact that Flex doesn't support extension managers. If you have libraries and you'll like to distribute the best way to go will be create SWCs, add documentation, package in a zip and uploading all this to RIAForge.org
MXP files do not appear to be any variation of ZIP archive format.
I will be using whatever as long as I can make use of the component itself, which is packaged as an MXP. Inside this MXP there is an MXI file too. I do not have any control over the distribution format of this component, these are developed by another party. All I need it to make use of the component(s). If this involves opening the MXP, extracting the MXI, and getting an ActionScript or SWF bytecode out of it, fine. I really do not care much for the format, I just need my application to make use of the component itself.
Are there any tools that convert an MXP package to something less binary perhaps? Or something that Flex can use at least?
After all the component is the same bytecode that Flash Player uses anyway, compiled from either Flex or Adobe Flash.
Try MXP Lister
I can't use MXP Lister because it is for Windows.
I am using Linux.
Does there exist MXP format specification anywhere?
You'll need the Extension Manager to open/install mxp files as that's what they're intended for.
Don't think there's a linux version though.
In any case, mxp's are not meant for use with Flex, so even if you'd manage to extract the components you may not (and probablty won't) be able to use them in Flex, especially if they're visual components.
At best, you can ask for a Flex compatible version of the components to whoever developed them.