When do you expect the extensions to be available?
Can you tell me when you expect the extensions to be available?
It may not be officially supported by the Vivaldi team but, I found that you could sideload chromium and google chrome extensions into it!
They've already mentioned they're working on an extensions interface (the ability to accommodate certain extensions is already inbuilt, and I have already installed one of my critical ones) and so I shouldn't think at least early extension support is more than a few weeks down the road, since they've provisionally committed to releasing a build a week. I would guess the two elements their mature support will have to address first will be signaling the Chrome Store that the browser is, or is like, Chrome, and then equipping the browser itself to differentiate and tell the user whether this or that extension in particular is actually supported.