Simon 5 is coming soon!
Simon version 5 is currently in beta testing. It is a massive update, introducing a much-requested feature: syncing the Simon data between multiple Macs, plus a Simon Status service, a Link Checker filter, improved Find filter, iMessage and Speak Error notifiers, a new app icon, and much more.
Important: please note that Simon 5 requires a minimum of macOS 10.12 (Sierra), and will be a paid upgrade from Simon 4 after the beta. Purchasers since September 1, 2020 automatically get a version 5 license (that also works in previous versions).
How about forwarding?
You are correct that the notifier doesn't include any settings for remote notifications. But, I think it should be easy to setup none the less.
The Growl preference panel allows you to setup notification forwarding (at least as of 0.7.6, the version I have installed on my machine) under the "Network" section. Assuming both computers are on the same network, you should be able to setup your Simon notifications to forward to your other machine. I hope this helps, and let us know what your results are.
Daniel