It's funny because imgur is actively trying to eliminate the gif format, even if it does with a convoluted wrapper format.
On blocking animated images, I should check in Vivaldi's settings if it is there, but I don't want to :/
And on the gif ending... It's simple, make a format that's as immensely portable and easy to use as gif and you'll probably make it work. That means stuff like easy embedding on forums for example.
EDIT: On the comments of that commitstrip, one person mentioned APNG (which is something that's literally in the PNG file format definition), but apparently only firefox and safari support it. Vivaldi isn't on the list but for this appliance in particular Vivaldi could act as Chrome, which doesn't. The question becomes "when's APNG support", rather than "when's gif ending"