Hello,
As you know, DollKart's online functionality is defunct and it cannot be updated. This doesn't mean that new things haven't happened. Steam has recently introduced the "Remote Play Together" feature. This allows you to play 2P mode over the internet with your friends, even if they don't own DollKart(though they should).
2P mode is something special as it's what the game was originally designed around, but the main issue was we couldn't get it to work online. Now thanks to Valve, it works. Grab a friend and give it a whirl!
Do note, you need a pretty fast connection and there is no matchmaking of any sort. This isn't an official online mode, sadly. It still does work and it still is fun though.