Java/C# are different in that they compile to a bytecode which is like vm assembly its also not meant as a high level programming language(note that this isn't always compiled to assembly at the end as it can be interpreted, standard java for instance does both jit and interprets for best results).
"Converting programming languages really doesn't serve any purpose whatsoever"
Compilers are useful.
This probably won't reach production quality but that doesn't mean it couldn't with the right effort, see hip-hop or one of those x-> javascript compilers.
Try http://www.eclipsecolorthemes.org/ (note I used it with cdt and had trouble with dark color themes making some elements nearly invisible) but other then that its sorta nice
Something that legally prohibits this falls outside the definition of open source. Dual licensing with part of it not available as open source can fulfill your need although many including me somewhat dislike that and consider that against the spirit of open source. The GPL prevents people from modifying/distributing modified source without releasing the source and is highly disliked by a number of companies who would have nothing to do with it. They can still use it without distributing it like on a server without releasing changes as open source.
reference counting is slower* then other forms of gc.
My guess why its fairly fast in c++ has a lot to do whith how much you can avoid it by allocating things on the stack(of course you can do escape anaylsis but most gc'd languages don't have explicit stack allocation of non basic types)
I think you are greatly understimate how great less relevant ads are.
Much less data/less identifying data gathered -> slightly less relevant ads and a huge win fore everyone. Not that this will lead to that but it would be great if it did.