What are the benefits particularly?
I've heard it's more efficient, is that in terms of bandwidth? I've also heard it will allow for block and I believe transaction notification, which currently must be done by polling.
Are these the only two benefits?
Are there any security implications with replacing the json-rpc system with 0mq?
Is the current RPC system going to be left in place to support backwards compatibility and legacy systems?
I cannot speak to all of the pros/cons of using zmq, as it was decided upon before I started work on it.
So far, I'd say that if you use it well it gets out of your way, but does all the networking things that are simply tedious and error-prone. I'm sure there are other solutions that are adequate for this, but zmq seems to be pretty good and is available on a lot of platforms/languages.
I don't know that it will be more efficient for bandwidth, that's difficult to say. I think long-term it will be far more efficient for developer time when someone comes along and wants to write a service that uses the RPC, and to me that's very important to get right.
Backwards compatibility will be around for a while, of course. I'm debating whether that should be "simply keep the old RPC around for now" or "write a translation layer that translates the old calls to the new for less error-prone maintenance until the old is deprecated completely". Regardless of what it looks like internally, the old RPC should stick around for a while (and appear unchanged from the outside).
In addition to efficiency improvements over the current RPC system, OMQ will enable walletnotify and blocknotify functionality.
After OMQ is merged, the new RPC API notification can be made compatible with Bitcoin. This compatibility will help streamline Monero integration by merchants and service providers.
OMQ will also help facilitate RPC authentication and encryption making RPC usage more secure than it is today.
