The cost of such schemes should be considered against the cost of building and maintaining cities like Edinburgh. Good transport links would make Hawick a commuter town for Edinburgh, far better to build housing in Hawick than Edinburgh in my view.
Housing is going to be built in Edinburgh and the surrounding area - investment in transport is needed there. The forecast is another 50K people in Edinburgh, East and Midlothian by 2028; for the whole Scottish Borders just over 2000.
Hawick is too far away to become a significant commuter town - some people already there commute but people aren't going to choose to move to Hawick over places closer to the city.