If by that you want Vim to become compatible with Neovim Lua plugins, Vim will have to add and maintain compatibility with the whole Neovim non-Lua API as well (new functions, options etc). This will never happen.
Don't know which of you or the sibling is right. But even assuming you are, maybe display a warning or something, but let me disable the tabs. They're an absolute PITA. I would gladly buy more RAM to accommodate that.
For Firefox, I've found an extension that moves tabs to a new window. It mostly works, but there are rough edges. I apparently have enough resources for all my browser windows in my shaggy laptop for it to never swap. The overhead doesn't seem huge enough to warrant the removal of the possibility of disabling tabs.
Meh, window management is optimized to the hilt. The real expense is the web view, which you're going to have anyway, as these days all browsers use separate processes.
