Wouldn't it be a huge step forward if anybody could play LZ online? In chess Leela Zero offers such a chance already. How realistic could be an implementation?

Anybody can already, there a various Leela Zero bots running on KGS, OGS, Fox etc. Maybe not enough for everyone who wants a game to get one immediately as it's just kind volunteers donating their compute resource.

You are correct, and i add one "tygem baduk" of korea.
One thing is that except KGS petgo (always updated) all others did not disclose networks they use. I would like to see one of them employing facebook elf v.1 weight file. Up to now there is none. KGS petgo or the other one > 9 dan bot, their time settings 20 seconds would in favor of AI than of human. and 20s x 10 times won't help. I don't need 10 times, 3 times is enough if they are 30 second each.