Hello @smac, thanks for your comments!
Regarding memory profiling, we just published last week a really complete study: you can check it here. Also, have a micro-ROS middleware (Micro XRCE-DDS Client) memory profiling, check it here.
As you can see, there is a lot of potential room for improvement, but we are working hard.
Regarding the Unos and Megas, they are 8 bits MCUs with very few RAM memory… maybe just an XRCE-DDS Client app could fit. Internally we are thinking about a mini layer on top of XRCE with the same RCLC API, maybe it is a cool possibility for this tiny 8-bits ARV.