Currently there's no real way for component developers to include their own com_xxx.php file in their own folder. Not sure if it was designed to be this way but wouldn't this help or increase more integrations from existing components.
By allowing an extension to add com_xxx.php in their own /administrator/components/com_xxx/ folder, developers wouldn't need to include their files in the /administrator/components/com_jupgrade/extensions/ folder. In a way, JUpgrade will scan the file listed in this folder say, j25upgrade.php or com_xxx.php and use this file instead.
Currently there's no real way for component developers to include their own com_xxx.php file in their own folder. Not sure if it was designed to be this way but wouldn't this help or increase more integrations from existing components.
By allowing an extension to add com_xxx.php in their own /administrator/components/com_xxx/ folder, developers wouldn't need to include their files in the /administrator/components/com_jupgrade/extensions/ folder. In a way, JUpgrade will scan the file listed in this folder say, j25upgrade.php or com_xxx.php and use this file instead.