No current way to use terraspace all up and connect stacks from different TS_ENV. Dug into this a while ago and it’s quite complex. It’s because TS_ENV loads super early in the terraspace boot process. Configs like config.build.cache_dir need to be set up quite early. Unsure on approach with it 
Will review and consider PRs. Of course no sweat either way.
The post you found How to use outputs between Multi Region stacks - #2 by tung is non-ideal. Haven’t figure this one out though.