This is the line I mentioned in an earlier thread. I rode it to Tweedbank and back a couple of years back when I was briefly in Edinburgh. Nice little ride. Hopefully some day it will get restored all the way to Carlisle.
Scotland has also reinstated service on an additional Edinburgh - Glasgow route that had been out of service for many years, and has of course aggressively electrified almost everything between Edinburgh and Glasgow. The Edinburgh Waverley - Glasgow Queen Street service that runs every 15 inutes via Falkirk is truly impressive in terms of frequency, speed and convenience.