Judging from the code, the main idea is to implement the Arc (or Arc-like) language using the standard techniques used to implement new languages in Racket. This approach will make it easy to use the tools/infrastructure of Racket without any changes (correct highlighting, arrows between a variable and its binding, scope aware renaming of variables, profiler, etc.). The new language compiles via macro expansion to Racket which is then compiled and jitted as normal.
If I recall correct the original implementation of Arc was written as an interpreter - and thus the Racket set of tools are not available.
The main benefit is that the new language will run faster than standard Arc.
As a bonus it will be possible to use module written in Rark from Racket code - and use modules written in Racket in Rark modules.
A more developed variant with these goals, that got discussed a fair bit in the arc forum, is https://github.com/arclanguage/arc-nu. It hasn't received much kicking on wheels by anyone other than its author(s), though, so be prepared for some rough edges if you decide to try it out. In the long term I think it might be much nicer than the original prototype.
If it's helpful, the original implementation of Arc was actually quite similar to this - a bunch of macros that compiled down to MzScheme (which eventually became PLT scheme, which eventually became Racket!).
I found Arc version 3.1 on arclanguage.org. It does compile to (Mz)Scheme - but it does not use the MzScheme macro expander. It reads Arc program as an s-expression. Compiles the program and produces an mzscheme program also represented as an s-expression. The "problem" is that s-expressions doesn't track source location of identifiers. That made it impossible for the old Arc implementation to reuse the MzScheme tools.
Some the libraries were written using Arc-macros that expanded into simpler Arc constructs, but MzScheme macros weren't uses in that process.
Note: PLT Scheme was the names used when MzScheme, DrScheme and a few other tools was distributed together.
The Arc programming language [1] was created by Paul Graham (and Robert
T. Morris). Arc was used to create the original "Startup News" site which eventually
became "Hacker News". Kogir is one of the developers at Y Combinator
that currently works on the HN code.
If I recall correct the original implementation of Arc was written as an interpreter - and thus the Racket set of tools are not available.
The main benefit is that the new language will run faster than standard Arc.
As a bonus it will be possible to use module written in Rark from Racket code - and use modules written in Racket in Rark modules.