Into what format in memory? You can't just mmap into a parquet file and access whole records, it's a columnar format.

Arrow is absolutely designed for Interop between languages - often devs want to develop their core in something like Python, and the platform devs want to work on Scala. Arrow lets you write all the distributed system and data shuffling in Scala, but then users can access the same records in their user-defined code with minimal overhead