Here is the text of section 13. I think you are badly misreading it: > Notwithstanding any other provision of this License, if you modify the Program, your mo

Here is the text of section 13. I think you are badly misreading it: > Notwithstanding any other provision of this License, if you modify the Program, your modified version must prominently offer all users interacting with it remotely through a computer network (if your version supports such interaction) an opportunity to receive the Corresponding Source of your version by providing access to the Corresponding Source from a network server at no charge, through some standard or customary means of facilitating copying of software. This Corresponding Source shall include the Corresponding Source for any work covered by version 3 of the GNU General Public License that is incorporated pursuant to the following paragraph. First of all, it says "your version" has to offer users the ability to download the source. Clearly, a sticker with a URL next to the midi jack would comply. However, it only applies to remote users, so your example is already limited to the corner case where they are connecting to a remote midi device through a network port that doesn't have a UI. Even then, the license says "if your version supports such interaction" which could be construed to be referring to the phrase that follows the disclaimer instead of the one that precedes it. Even if you read all of those things in the "you have to serve source code over the network that serves the remote midi protocol" way, the clause "through some standard or customary means of facilitating copying of software" clearly implies that you could (say) offer it over port 443 on some server you run, or via a github link. In fact, that clause pretty clearly means that only distributing it through some obscure MIDI extension would not put you in compliance with the license.