While strict anonymity can be seen as a preference to a user attempting to conceal all aspects of their identity, it is infeasible and impossible to say the least. Tor, Blockchain, and other anonymizing technologies designed for a specific purpose can never be made to be infallible. After all, people do make mistakes and those are the elements that lend to defeating the security of a given program. As has been focused on, quantum technology would, undoubtedly, eradicate most of our current encryption technologies and render them useless.
If we are looking to define the type of anonymity offered by technologies like onion routing and blockchaining, then one definition could be platform specific anonymity—where anonymity is not defined as strict, but as a component of that given platform that is either difficult to defeat or cannot be realistically defeated with today's technology.
Defining anonymity as undefeatable stretches the purpose of the term in my opinion. Here is the general definition of the word anonymity as per the American Heritage Dictionary (found on Free Dictionary):
- The quality or state of being unknown or unacknowledged.
- One that is unknown or unacknowledged.
Anonymity does not refer to the quality of being incapable of being unmasked, merely the quality of being masked. In Information Security the ultimate goal is to protect a user's information to the best of one's abilities utilizing anonymizing software that is known to be effective by today's standards. Any security mechanism can theoretically be defeated, especially by a determined adversary with enough resources at their disposal. Tor is not perfect nor is Blockchain, but they offer a level of protection that is currently not simple to defeat (though Tor has definitely seen its browser compromised in the past as well as its nodes poisoned).
 For the American Heritage Dictionary definition:
American Heritage® Dictionary of the English Language, Fifth Edition. S.v. "anonymity." Retrieved April 20 2018 from https://www.thefreedictionary.com/anonymity