I'm interrested to know if some people are actually trying to use 4 RB5009UPr+S+IN with the K-79 rackmount kit in their setup?

myself I'm tempted to replace my current design by it. The current design is using a CCR2004-1G-12S+2XS as a core router handlinkg2 uplinsk using BGP. This router provide the connection to 4 servers behind a 10G switch (the CRS317) getting themselves their connection using BGP and a unifi UXG router used for the lan statically linked:
This to separate the LAN from the locally hosted micro-pop.

My idea is to use the RB5009UPr+S+IN to replace the POE switch, Unifi router and the CCR2004.. 2 routers will be each connected to 1 Uplink uing BGP, They will be powered by the 2 others using POE. These 2 touters will be electrically connected using DC. They will also handle the APs. Each router would be connected to the switch using the SFP+ port. The idea of this design is to increase the resiiiency (2 roursers to get the connection and reduce the power usage. Thoughts? And you how are using your RB5009?

I'm all for reducing complexity and electrical costs. I've only recently started to play around with the RB5009, but its not the all PoE out model like you've got. I'm sure you know that power in on this unit is what goes out. So, keep that in mind with your design. I like to look at the block diagrams and make some decisions from that. How much data is coming from which port to where, inter-vlaning decisions, etc.