Well yes you could add a new border style that would be "like 3 but more sensible", then you'd just have people with old renderers getting no borders at all. I think.
Either way, it's not really something that starts with Aegisub. Your best bets for getting in contact with current developers that touch VSFilter and libass would be the MPC-HC, VLC, and mpv projects.
Do not PM me asking for help with Aegisub, Automation, karaoke or anything like that, I won't reply.
Ask your questions in the public forums. Use the Search function, somebody probably asked the same question before.
All rights reserved to call you insults if you ask poorly thought out or redundant questions.
Experimenting is free and is a great way to learn things.