I think these are good ideas and I appreciate the amount of thought you put into them but one major issue I see with this is compatibility. Other clients will have to implement these features for it to be more useful. If the developer decides to add this, these should be made into open standards(in this case BEP / BitTorrent Enhancement Proposals) to encourage other clients to adopt them. While helpful, an open standard does not require code to be made open source. It just has to be very well documented and explained. Example code is very helpful but not absolutely necessary. I would understand if the developer doesn't want to release any Tixati code even if it's just for these BEPs. I'm calling it a BEP because it should become standardized and not remain just as a feature exclusive to one client. I think a messaging BEP is somewhat important because the decentralized chats some torrent clients offer are all fragmented. For example, BiglyBT offers a DHT based chats/messages(similar to Tixati) but Tixati users can't talk to BiglyBT or other clients. This is going to take a lot of work, planning and testing. It would be nice to have and I don't like sounding pessimistic but I don't think it will happen unless enough people work on it. If someone else made the BEP and it reached accepted or draft status than the Tixati developer would be more likely to implement it. I think this goes without saying, but the messages should support Unicode(any language) and not just ASCII(a-z, special characters).
Here is a list of BEPs if you're curious: http://bittorrent.org/beps/bep_0000.html
You are probably familiar with some or most of these like UDP trackers, uTP, DHT, etc..
For the messages, I think there should be some sort of limits to mitigate spam. I think message filtering should only be done by the client. If there is any message filtering in the BEP it should be very very minimal because if it's too much it would feel too restrictive in my opinion.
general filter example for everyone:
(ignore FROM any) individual messages exceeding 200 words
specific filter example for a spammer:
(ignore FROM specific IP FOR 24 hours) block/ignore all messages
rate limit filter example:
(ignore FROM any) messages exceed 65 per minute
(accept FROM specific IP) ignore above filters