[Typo in onion list address, fixed and resent herein]

The descriptors seem to indicate onion addresses. So if I act a relay, I seem to be able to get the addresses. Then how? ... Could someone skilled try to get the lists? :D

Yes, many services, researchers, and privates routinely do this. The code exists in some repositories, or you can write your own, it's not hard. Enumeration and listing in and of itself is not a problem, neither good nor bad on its face, a mere fact of the technology in use. It's up to the v2 users to decide if the tech works for them or not, fits their use case or not, and whether or not to use it, not use it, or use something else, or to seek or be provided education on the tech and tradeoffs. For many users, v2 vs v3 simply doesn't matter. For others, you may wish to blog or help them choose v2 vs v3. And in fact, v2 onion services are very useful when combined with OnionCat to yield IPv6 and UDP transport among tor's P2P onions. That's simply not possible with v3's no-IP TCP only onions. So for example, VoIP and other existing and new comms apps, mossh, and Bittorrent freespeech and robust uncensorable distribution channels, are enabled and exist entirely within tor's v2 onion space, somewhat similar to I2P. Search the list and tickets for "onioncat" for other use cases. Just because some poor souls footshoot themselves... which they'll still obviously somehow mangage to do with any tech regardless... isn't sufficient reason to cease support, maintenance, development, backporting, and furtherance of an agnostic technology such as v2 onions.

with OnionCat to yield IPv6 and UDP transport among tor's P2P That's simply not possible with v3's no-IP TCP only onions.

That is to say, it's not possible with code that exists today... the various possible solutions, and others yet to be proposed, that could provide those things with v3 onions, haven't been developed and put into working code yet. As such, it would be an interesting project for anyone or group that wants to do it.