So if it can do 4k over two lanes at 60hz, does that mean were finally talking 4/5k resolution at 120hz being possible assuming we utilise all 4 lanes?

connector will very likely be same, because it already has 4 lanes for data streaming. But it is more question of frequencies at which graphics card can transmit data without error. But if GTX970/980 is not released as DP1.3 compliant then it will not upgrade just by vBIOS update.

Well... I'd like if my DisplayPort 1.1 laptop was updated to 1.2 😀 No, it's not that easy. We'll see if GeForce 9xx and Radeon 3xx will be able to support such bandwidth, and more important - if it makes any sense, as we're talking about lots of pixels, and today it's difficult to play at high frame rate even at 2560x1440, not to mention 4k or 5k. Even SLI/CF systems would struggle. Adaptive VSync will make things easier, but nonetheless it's not an easy task (with 5k@60fps we're talking about 885 millions pixels per second).

+1 Being a mid-range gamer my next monitor will probably just be a 1080p 60Hz panel (currently still rockin my old 1680x1050). But I would love if I could get one that supported DP 1.2a or 1.3 without paying a huge premium.

We just have to wait a bit. I think it's a really bad time for an upgrade right now unless one has a lot of money to spend. I'd upgrade when adaptive vsync gets better (if any) adoption rate, so you'd be able to get way better smoothness-to-cost ratio. And at that time, USB 3.1 should be available too.

4k @ 120hz (or more). Hazzah!