FWIW, it looks like the biggest changes for TOML 1.1 are allowing tables to span multiple lines, and allowing trailing commas. These seem highly likely to creep into hand written files.
Builds tools should probably warn about 1.1 features and potential compatibility issues for the next few (five?) years.[1]
But I don’t see any actual users being happy about a complete ban - that’s just what spec authors like to do 
How to do this is left as an exercise to the tool authors… I guess parsing in 1.0 mode and falling back to 1.1 mode is the way? Which requires library updates and work and etc. etc… ↩︎