@Suiseiseki https://www.eclipse.org/legal/documents/eclipse-openvsx-publisher-agreement.pdf

It says under section 3e that you can't require compensation for your plugins when they're distributed on the registry, but those appear to be terms for the use of the repository as a publishing service, which I think are fair. It wouldn't restrict you from publishing or charging money for them elsewhere.

Under section 4 it says that plugins must be licensed and those without a provided license will be distributed as MIT-licensed, but nothing about restrictions on the terms of the license that you choose. I could not find anything that would grant them the ability to relicense anything you've published.