I would like to suggest a Site-to-site filtering to choose between usage of VPN tunneling or bypassing VPN.
The problem in China is that there is censorship based on DNS/IP address. The router app allow us to tell if a device should use all its traffic through VPN or not. Another layer would be interesting to improve that.
I think maybe some more "techy"-people got a similar idea (last time I did this kind of thing was with an "iptable" command, 15years ago) but I cannot formulate it in a better way since I don't know much about Tomato firmware.