I’ve never used Tridactyl, but I switched from vim vixen to qutebrowser and found the full browser allows a much deeper vim integration and customization than a plugin ever could.
I’d highly recommend checking out qutebrowser if you are interested in this type of thing.
One thing that made me stick to tridactyl is the lack of addon support in qutebrowser, and I don't use that much addons: privacy badger, multi containers (especially this one), cookie auto delete and unlock origin ...
I'm still not sure what exactly Privacy Badger really does under the hood, but I suspect much of it won't be possible with QtWebEngine's API.
Not sure about Cookie Auto Delete - I fear it's not possible to implement either, but I'm not entirely sure, I've always found the QtWebEngine cookie APIs quite confusing so I'd need to take a closer look.
I’d highly recommend checking out qutebrowser if you are interested in this type of thing.