Well, the advantage of allowing new Unicode/ASCII symbols is probably not obvious at first glance. As you could observe with emojis, a community formed around their use much later, which was totally unexpected and yet is now one of the main features in the entire community.
The same is to be expected with “_” or “$” or other ASCII symbols. The latter also makes sense because currencies are one of the main applications of Ethereum/Crypto.
Especially in the area of subdomains, for example “Ξ.kraken.eth”, “€.kraken.eth”, “$.kraken.eth” are certainly a very good application in terms of wallet applications for stablecoins or exchange wallets. But that is only one of many applications that could be possible.
Similarly, domain names with underscores are another creative freedom in choosing one’s Web 3.0 identity to give to the community, besides the technical reasons Nick mentioned. They do fit in nicely in my opinion as rank.eth pointed out aswell.
The point is that we can’t know in advance what creative developments will come up, but we should at least give the community the opportunity to use these symbols without being overly restrictive, this is what makes ENS so different and successful.
I think Raffy made a good point in his other thread. We won’t be able to prevent the number of domains that clash with Web 2.0 DNS from increasing anyway, as people will surely come up with the idea of simply registering punycode literals in the future (why wouldn’t they), that alone will lead to the list of incompatible domains getting bigger, besides the fact that different browsers use different standards for insufficiently supported emojis/Unicode anyway. However, as the number of these domains is very small in the overall context, this is not a problem in itself.
The solution, as Raffy has already mentioned, is to tell the user at the time of registration whether the domain is compatible with traditional DNS or not. But the solution, in my opinion, is not to live up to old, worn-out rules forever and ever, the importance of which will continue to diminish in a Web 3.0 context anyway.