we are receiving some queries on sub-menu extra customization; and we can understand that our users want to have more options: recently we had a few threads, regarding the submenu customization option and we can understand that it becomes increasingly valuable feature for our creators, you feedback will be forwarded to our developers
As for the custom solutions with Velo, we can offer mega menu customization with some API here:
https://www.wix.com/velo/example/mega-menu