Hello all! Happy to report back here that tables now have a new getDisplayData() method which allows you to programmatically access any filtered data from your table in JavaScript queries (including custom columns and mapped values 
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It is an async function and will not work in transformers, but in your JS query you can run
const displayedData = await yourTable.getDisplayedData()
which will return an array of objects representing the currently visible data on your table 