Chinese Elm Trunk Decay (Looking for solutions)

[Contact]

Time for ye olde die grinder… aka Dan Robinson

Cheers
DSD sends

Agree with you

 

[Shibui]

hollow out and connect the holes, which I could do at this point simply by poking through the dead wood. I'd end up with a Swiss cheese trunk though, and have little experience with a grinder.

I doubt you'd need a grinder. The wood appears so well rotted you'd probably only need to scrape out the softer parts with a pointed stick or large nail. Natural hollowed wood usually looks so much more natural than carved.
Definitely no need to act immediately. The tree's life is not threatened so you have plenty of time to consider, research and seek further opinions.

 

[oranjeaap]

Prevent new water from entering the cavity. Poke a hole near the lowest part of the cavicty so moisture can escape and increase airflow.