Bitcoin will never scale without Litecoin. No significant protocol changes will ever be made to Bitcoin. Bitcoiners need to get this nailed into their thick skulls. Read the following:
Bitcoin will achieve maximum value by enabling SegWit on Litecoin. There is no other option going forward. The above linked post explains why in detail.
How would this be possible without some type of protocol change that allows stuff such as atomic swaps? Without that the chains are stuck as separate entities.