I would rate the chances of this option becoming available as very remote. Not that no one wants to do it, as I am sure there would be a good bit of interest. However, it its design, support and maintenance would be a nightmare, and no matter how good you are, it would fail for someone (usually someone who has done some custom work on their Trixbox) who would warn everyone not to use it.
The issue is that Elastix is not just one product with a version number that covers all component. Trixbox is similar, depending on what versions of products that you have one there.
Your best bet if you have many Trixbox systems to convert is to either
1) Only concentrate on Freepbx and do a backup and restore from one box to another. This will definitely break things.
What I did with many of the trixboxes is bring all the Trixbox up to the latest version possible, update Freepbx to the latest modules, installing all modules. So in essence you are taking the backup from a particular version of Trixbox (or as close as you are going to get it).
Now choose a stable release of Elastix. Don't do a YUM upgrade to it, just update the Freepbx with the latest modules (don't go to Freepbx 2.5). Again now we have a Elastix system with a known version (or close).
Now do a restore to Elastix via Freepbx and look at what breaks....start the repairs. It is important to have a working system as well, so you can compare the broken system to what a fresh system looks like. Write down everything that you correct as you do it, and then follow the same fixes for each of your machines.
It may sound onerous, but it can be done. The first box took a few hours, but many of the others took less than an hour. If your systems are less than 30-40 users then look at option 2.
2) If the system that you are converting from has less than 30-40 extensions, rebuild from scratch on a separate ELastix system, rebuild Freepbx configs offline, backup the freepbx, and then restore onto the new Elastix system that you just installed overwriting the Trixbox install. Naturally, if you are smart, you would have purchased a new hard drive, leaving you a roll back plan.
As I said, it would be nice to have a tool, but highly unlikely to arrive, and hell of lot of work for almost no return except a few brick bats when so ones install goes South, but the above methods do work and have done them many times as we upgrade many of the older systems. Personally I like the brand new build, knowing it is fresh and will present me with no hidden errors in the future (or at least none caused by my upgrade).