I am not an expert in Rust's mechanics and only looked at it superficially, but I got the impression that shared references can't be guaranteed (to not exist in mutable ways) all the way through an object graph. I am not surprised if I am wrong about that. It wasn't the main deciding factor for me...
My primary factor was "Actor Model" and I was struggling with Erlang's lack of static types, so that put Pony in the focus. An Actor Model framework on top (I recalled there was one for Rust) had given me "questionable" results with Akka (due to compromises/constraints in the JVM and Java/Scala).
As a regular Pony user, and coding seriously in it for a few months, this is what I think;
I rather fight the Reference Capabilities (easily the hardest aspect of Pony and probably the number one reason people give up) than to spend endless amount of time CHASING concurrency problems, or even worse, HOPING that I didn't forget some lock/mutex/whatever and ending up having data corruption.
Pony is forcing me to do the right thing, and doesn't allow me to "I guess I could get away with X", and this reassurance is a huge boon.
It is hard to learn, and if you are not in the concurrency space, don't know what a thread is and don't care much for data integrity, then Pony is not for you. The effort you need to put in will not be appreciated by you.
If you have a strong opinion on how things must be done, Pony is not for you, because it won't allow you to follow your opinion all the time, because the opinion is not safe.
Pony is not for everyone, but for those that can think in the Pony model, then it is an incredible tool to ensure your code is correct, safe and performant.
So many comments, have not read through them all. There are so many cool things to stick your head in, so you ask if you are getting too old; YES. I am 46, and predates your career by 15 years, and I am still fascinated over the new possibilities that presents themselves year after year.
Sharing of ideas in Open Source; Happens all the time, maybe it is now too technical for you to follow, and family interests keep you from digging in enough to catch up.
Sharing of ideas of the future; Happens all the time, in blogs, tweets and what not. In fact, we are getting drowned by so much information that it becomes a challenge to filter the noise. AND you have a new idea right there; Give me something to filter the garbage out and serve me the gems on a plate. Such tool itself will accelerate ideas collaboration even more.
Privacy concerns; Centralized so called "cloud services" at various levels are going extinct in the future, because of privacy will become a massive sore points, possibly after some scandals (need to brew a decade or so for full effect). So, prepare social network system that is truly distributed and where the consumer control exactly what is shared with whom and how, and can take it off-line...
I think over a week-end with a lot of supply of beer, I think a group of visionaries can come up with 10-20 solid new things that is both doable, and should inspire people who like to GetThingsDone.
So, the final question to you; Are you the consumer or the producer of the great things to come??
My primary factor was "Actor Model" and I was struggling with Erlang's lack of static types, so that put Pony in the focus. An Actor Model framework on top (I recalled there was one for Rust) had given me "questionable" results with Akka (due to compromises/constraints in the JVM and Java/Scala).
HTH