What mode is this?

It looks like a glitch to me. It's the SR map with the Dominion vision and capture points. My guess is a bug in the spectator replay system (especially with the ridiculously high damage numbers shown), but I'm not discounting the possibility of a new Featured Game Mode. I don't have PBE access, so I can't actually say either way.

Some client side hack that they use to showcase skins. There's no turrets and you can see the other area up by top jungle creeps they use to compare two skins side by side.