I heard that the T5 Playtesters got a CD of preliminary T5 material in early 2009, which is a couple of years ago now.
2008. But some material goes back another year, to 2007. And as Ishmael noted, he's been thinking about it for at least 10 years. Actually longer.
Have there been any further developments since then?
Release of the updated ship design system (December), animal creation system (February), and work on equipment.
As TashaG noted, it'll be released when it's ready.
I don't know what's left to be done (besides some lists, like an equipment list for example) but that doesn't mean it's ready.
TashaG also brought up Mongoose Traveller. I think there's not much competition between the two systems. For one thing, Marc has no desire to undercut Mongoose -- after all, MGT is an investment on his part. For another thing, Mongoose has churned out adventures and supplements, some of which are generic enough to be useful for any version of Traveller, including T5.
I think T5 is a better-integrated resource, with interrelated toolkits which work with common benchmarks, and a rules system that makes use of those benchmarks.
And there are some interface points between the two game systems: Mongoose starships are usable in T5 (as are Book 2 starships), and PC weapons and armor created using T5's makers can convert to Mongoose numbers with a simple lookup. Similarly, you can use T5 to generate vehicles and robots for Mongoose. The most noticeable difference between MGT and T5 is in how skill levels are distributed -- and to some extent Mongoose skill levels map to T5 skill levels by simply adding to them.