It would seem that 4.3 will be released soon.While the link pertains the end of PvP season 10 at November15 those seasons and PvE related major patches tend to follow eath other very closely. My estimate would be one week after season 10 is finished, so November 22 (or 23 for us in Europe).
Such an estimate would also correlate pretty well with the PTR receiving a Release Candidate.
Anyway, what will 4.3 mean for us pugging tankadins? Not all that much it would seem. Let's put the new content aside for a bit and just look at the tankadin. While Blizzard has decided to make a major overhaul come MoP, as the do every Xpac, they'll let us keep our rather insane mastery for 4.3. Say hello to 102.4 even as a pugadin. At the other hand, that also means if you take an unmitigated hit, then you'll be considered doing something wrong.
So we'll continue to be the holy tin-can with an oversized barn door as extra protection for, say another half a year or more. I'd guess they'll slap in some kind of micro content patch late 4.3, like the very last dragon-raid during WotLK. And, as usual, I expect whatever new mechanics are being implemented in MoP to go live in Cata around a month or so before MoP is released. So don't expect a major overhaul of our abilities until August - October 2012.
With Blizzard losing subscribers left and right I don't expect them fo keep us running the last major patch in Cata for a full year. That would be akin to corporate suicide, so I might be too pessimistic when guessing at August - October. But then, who in their right mind would even consider releasing a major patch for a computer game in July -- oops, ok, maybe, after all.