tl;dr Proton Visionary is our exclusive plan for early supporters. It gets its name from a group of crowdfunding contributors who donated significant funds(new window) in 2014 to make Proton Mail possible in the first place.
With Visionary, you get access to all our premium services and features at their highest limits: Proton Mail, Proton Calendar, Proton Drive, Proton Pass, and Proton VPN(new window). You’ll also receive at no extra cost the paid versions of all new privacy services we release in the future, along with early access to all future features and products.
I have Unlimited, it's just me for users, and I haven't maxed out my storage. So doesn't seem worth it (nor Family) for my use case. A shame as it does sound like a good deal.