Q:

supporting lz4 compression with json format

it's more a feature request than a question. 
LZ4 is one of fastest known LZ77 compressors today and is especially efficient when decompressing data. Its compression ratio is not like of gzip but is very good on text data. It's so good that it can actually save user time when writing a file to a persistent disk compared to a raw write in IO scarce environments like Google cloud.
Also it can save lots (lots!) of CPU cycles to Google and its clients if you guys support lz4 for uploading the data in addition to gzip. 

A:

This question is a feature request which would belong in the Cloud Platform Public Issue Tracker [1]. As a stackoverflow question, though, it's somewhat out of place. I encourage you to make a feature request which explains your use-case in the public issue tracker, while asking specific technical questions on stackoverflow. If you have any questions, you should refer to the Help Center [2] [3] here on stackoverflow or check out the kind of issues and feature requests which get reported in the App Engine public issue tracker [4], for example.

