Topic on Help talk:Tabular data

Would it be possible to increase or abandon the 400 char per "cell" and 2MB overall limitation? What would be the correct place to discuss this?

It is definitely not possible to extend the 2MiB overall limit, no; that's a fundamental limit from MediaWiki. If you're dealing with that much data, this simple system is probably not right for you.

For the cell limit, I'd suggest a discussion on Commons about making such a change and then filing a Phabricator task asking for the change.