The new spring of 2020 product guide has been released

Just had a browse of that. It looks like the K series NVR's have gone and been replaced by Q series which will have NVR 4 by default I suppose. Although you can install I series NVR 4 on the K series it runs like a pig and seems to be buggy.
 
I think the K model NVRs have been out for quite some time now and have shown their age. Hence their discontinuation.