What you are describing is simply encrypting a message to multiple recipients. I don't think we should ever have such a thing in the blockchain unless there's a very good reason.
I respect your work and I especially respect anyone who would have Gnosis as a username, but let's back up a second.
Anoncoin is respected as an attempt to add an additional face to the spirit of the anonymous collective, individuals who have certain values. The financial anonymity of the coin has very little to do with that spirit. Anonymous financial options are available to those who want them, in several coins. Financial anonymity is important but should never become the core.
Sharing information without the intrusion of gangsters, including and especially those in govt, is far more basic a right than sharing, spending, etc money anonymously.
This goal is very important to me personally, but a blockchain may not be the right tool for the job. Also, there are existing products, such as Syndie, OTR, TextSecure, Freenet, and plain old GPG-encrypted email (to name a few) which could fill this need.
If your concern is with the general public not using such tools enough, I think it's not that the right technology has not come along, it's more that user interfaces and security education are both lacking. And for those who are not tech savvy coming up against a behemoth like the NSA, they're likely to feel completely defeated and just give up on the idea of having privacy from such an entity. We should fight this defeatism as well, somehow.
There are many things I cannot say in public. I have gone to jail and been beaten by police only for words, though certainly not to the extent that many other people have and are. There is lterally no country on earth where complete freedom of speech exists. In the u.s. of course there is the patriot act, famous for stifling speech and thought, but there are also secret provisions of the patriot act. You can commit a crime of word or deed without even knowing you commited a crime, since the fact that it was illegal was and is secret.
To add free speech, in any way, to a coin is worth more than adding the confidence that transactions are anonymous, when in fact they might not be. Every so called perfect tool that involves more than a few people is eventually found to be corrupted. We know the nsa and others have penetrated most encryption tools in one way or another. There have been news items about the nsa attempts to penetrate tor. Were they successful? Only they know. You can argue that tor or any other tool is unbreakable but there are workarounds, backdoors, for any tool that involves a network. All they need is one person to insert one small snippet of code and they own it all.
I think the recent discoveries of what the NSA has done and can do should make us all more careful with how we develop software, what software we install, etc., but it's not an impossible task to resist this. Intelligence agencies love automated snooping and hacking tools because they are scalable to billions of persons. On the other hand, automated tools can only do so much, and can be thwarted by a careful, paranoid person who knows software and hardware well. There are also targeted attacks, which can be very penetrating, but those require actual person-hours being devoted to it, so intelligence agencies have a limited ability to do those.
If the developers can stay anonymous, then it is much less likely they will fall victim to targeted attacks, since the NSA/GCHQ/whatever would not use targeted attacks against random Internet users that blend in with the crowd -- it's too expensive. Since developers have to pay for food, rent, etc., it's essential that they be able to send and/or receive money anonymously as well.
I guess this has turned into a rant, oops.
The best use of anonymity is for sharing information, not money. If necessary alternate blockchains can be used, a main blockchain for coin transactions and one or more additional blockchains for text that can be downloaded to run with the financial blockchain, if the size of the blockchain is the issue. Also of course the data in the encrypted blockchain should be strictly limited to text, since words should always be 100% unrestricted, while some other forms of data perhaps not.
A coin that allows reliable encryption of text as long as the computers are clean would be more useful than hiding coins.
Blockchain size is exactly what I'm concerned with. I think having text in an alternate blockchain is much preferable to encouraging this to be stored in the Anoncoin blockchain.