I recieved my kit earlier this week in the mail and only today did I start working on it. I got the basic frame assembled but i do have a few concerns with how it turned out. (not parts related just due to quality and straightness of wood here) I have been toying with this idea since I ordered the kit and figured that it may be worthwhile to help with keeping things flat/more consistent. Let me know thoughts/opinions 
Not knowing which router / sled / z-axis design, you may need to be able to adjust the placement of the top beam relative to the front surface (z axis movement) once you set your ring height in order to keep the chains parallel to the work surface. It appears that your 4 main supports are single pieces and that movement may pose a challenge. Other than that, It looks really nice. The cubbies at the bottom may collect debris if your dust collection isn’t just right, but it is a good use of space.
it looks nice, but might not be that practical because you might want to raise the top bar or make it longer or as Orob says adjust it back and forth for different thickness materials. if you are only going to use the middle 4x5’ area for cutting then the machine performance is improved with a higher 30" top bars if you are going to want the full 4x8 then the machine’s bottom corner performance works better with a 12 to 16’ top bar. your design locks you into something that can’t easily be changed latter.
Appreciate the input. Exactly why i posted as all replies so far are things that did not pop up in my mind!