I really like the chain-stitch/braided mainsheet, but it is a bit difficult to get the chain-stitched part through blocks smaller than 57mm.
To try and improve things, I am experimenting with a "composite" construction.
The chain-stitch is done using 3mm (~1/8") double-braid line instead of the usual 3/16". This line is not strong enough to handle the mainsheet loads itself, so a 3mm Dyneema single-braid line is used for the un-tapered part and woven through the center of the chain-stitch section to carry the sheet-tension.
This gives a slightly smaller diameter chain-stitched portion of the sheet (the primary goal). A secondary benefit is a smaller diameter line running through the blocks at the back of the boom.
Here's some more information:
http://performancesailingproducts.com/HiTechChainstitchMainsheetPrototype.html