I am reading this article: https://blog.torproject.org/blog/hidden-services-need-some-love
And there is a paragraph states that:
Defense against Denial of Service of Introduction Points
The adversarial version of the previous section involves attackers intentionally hammering the Introduction Points of a Hidden Service to make it unreachable by honest clients. This means that an attacker can temporarily bring down a Hidden Service by DoSing a small number of Tor relays.
To defend against such attacks, Syverson and Øverlier introduced Valet nodes in their PETS 2006 paper: "Valet Services: Improving Hidden Servers with a Personal Touch". Valet nodes stand in front of Introduction Points and act as a protection layer. This allows Hidden Services to maintain a limited number of Introduction Points, but many more contact points, without clients learning the actual addresses of the Introduction Points.
Valet nodes are not implemented yet, mainly because of the big implementation and deployment effort they require.
So is the use of Valet Node already implemented in current Tor, or is Tor still vulnerable to this type of DOS attack against introduction points?