1) Unfortunately I'm not familiar with this project or Meteor, so I can't provide much input
2) Yep, anything that can read JavaScript will be compatible with RapydScript, RapydScript output is fully valid JavaScript. The only gotcha is that I've recently dropped IE8 support in favor of standardizing ES5 features - so we're no longer compatible with ancient versions of JavaScript (because inbuilt methods/shortcuts rely on functions that didn't exist until ES5).
3) There are several features that fall into this same category (such as iterators and generators - which ES6 plans to add). The idea behind RapydScript is to bridge the gap and context switch between Python and JavaScript, I'm not opposed to features that help with this goal or make developer's job easier. I may not have the time, however, to add all of these myself. Community support would be appreciated.
4) Maybe, I don't use PyCharm myself (my editor of choice is vim, and more recently Atom), but would love to create a collection of IDE plugins if people could contribute them (probably as a different github project to avoid cluttering the main code base). As far as getting official PyCharm integration, I'm not sure what we'd need to do for that.