@y-okumura-isp thank you for sharing information!
with quick code scan, this design is similar with rclcpp::experipental::executors::EventsExecutor which already constructed on RMW listener APIs?
from PoC code, i see that main thread subscription just takes (Reactor, Not using RMW listener API yet) the data to the _msg and another thread which is created with user specified thread priority and policy processes the message once it is delivered. (there is no queue in the PoC sample, but i guess that we eventually need it.)
in that case, what is the difference if we use rclcpp::experipental::executors::EventsExecutor assigned with user created threads with specified priority and policy? (i think one of the difference is node object management to add the executor.)
according to thread policy and priority, probably REP-2017 Thread attributes configuration support would be interesting for you.