Will there be an update to LM5D based on the BS.1770-3 standard?
No. But this is actually not a problem with LM5D yet, as it's already fully BS.1770-3 compatible. The change from -2 to -3 was in the definition of true-peak level, but we have used the -3 technique even before it got standardized.
Furthermore, TC offers a reasonably priced cross-grade from LM5D to LM6 - click here for more information.