I am now in the curious position of owning equal shares in two good camera systems: Pentax and Samsung. As the NX setup can use adapted Pentax lenses I have kept my best ones - SMC 17 f/4 fisheye, a new-to-me SMC 55/1.8 and the M-series 85/2 and 135/3.5 primes. The M series especially was designed to be compact, so on a mirrorless camera they are excellent for both optical and practical reasons. I have two NX zooms and cannot imaging needing more: though the 16-50 with OIS and power zoom has a few possible advantages over the 20-50 I now have, price will not be one of them!
I have no Pentax body now, and I'm ok with that. the K-3 tempts, the K-01 and K200d beckon from happy earlier days, but too much fresh tech is about to emerge. Pentax now knows how to make a WR tilt screen (645z) and Sony makes on-sensor AF and better video possible. These items are here now on the NX300 but I expect Pentax engineers to do surprising things with the new technology. However they may not make the most of video updates, as they have stated they will focus most of their attention on the still image; I applaud them for it, yet I wonder if they will allow too many simple video features to be found elsewhere. The NX300's full-time autofocus and decent video results are not easily overlooked.
On the other -foot, Samsung is doing weather sealing now along with their ultra-hi-tech NX1. The Samsung sensors are now very good in areas they struggled with before, and they too could make more surprises visible soon. They even have nice pancake primes, in focal lengths that Pentax has not worked hard to keep in place (e.g. 24-30mm). So the only hard part for me will be deciding which system to buy in a year or two, when Pentax and Samsung are showing others the perils of resting on laurels or proceeding cautiously!