As things are, it seems much slower for simple operations. I added to some things to the benchmarks map and drop and map pred . map succ and map succ . drop 30 and got results like these

benchmarking map/map/foundation       49.63 μs  
benchmarking map/map/text             5.990 μs    
benchmarking map/map.map/foundation   98.84 μs  
benchmarking map/map.map/text         5.270 μs  
benchmarking drop/drop/foundation     258.4 ns  
benchmarking drop/drop/text           41.91 ns  
benchmarking drop/map.drop/foundation 46.39 μs  
benchmarking drop/map.drop/text       3.106 μs 

I'm not sure why the simple uncomposed map and drop work better. See https://gist.github.com/michaelt/b7e74602a52c0b36eb244c221e6177a8

It should be possible to write a Data.Text.Foundation that just uses the existing Stream operations for the cases where that makes most sense. It is just a question of writing stream and unstream functions. stream would look like https://hackage.haskell.org/package/text-1.2.2.1/docs/src/Data-Text-Internal-Encoding-Fusion.html#streamUtf8