This is actually extremely common.
For example, if you browse the UC Irvine ML datasets
https://archive.ics.uci.edu/ml/index.html
You'll find that many are in csv format.
If you do a search on data.gov
http://catalog.data.gov/dataset#sec-res_format
You'll see that it's about as popular as JSON.
Also, the World Health Organization
http://www.who.int/tb/country/data/download/en/
Also, many of the datasets at kaggle are in csv format.
https://www.kaggle.com/datasets
And this isn't that surprising, it's human readable, and gets the job done, and zipping will give decent compression.
I'm not sure who you think the target market for this would be, but I'm sure that if it's an efficient local format, you could probably get the ML crowd on board.