It would be above very poor, and could not load into a public lobby. When creating a friend or above lobby you would have a checkbox to allow them.
The intention would be to still allow crazy avatars like rollarcoasters while still stopping people form having insanely unoptimized avatars where they aren't wanted. This will put some pressure on creators to give the slightest care about performance, even if it's just "don't be completely insane".
The specifics is up to the vrc team but I'm thinking something like 600k poly, 300 mb vram usage, 30 material slots. I want to catch the worst avatars without catching the majority of avatars.