If there is to be a Metrolink route to Bolton, then one has to ask the question of what such a line would achieve and who would it benefit. Having lived close to the Bolton Bury line near Darcy Lever station as a child, and taking into account the vast amount of housing since built at Little Lever and Bradley Fold, that building over the track bed was a massive error, but it has been done, and I don't see a way around it. Also the bridge over Lower Darcy St, only recently replaced by a footbridge, and the bridge from the end of the Burnden Viaduct to join to the main line would also cause problems. Even taking the line down Manchester Road from that point would have problems. If we managed to overcome these obstacles, it may well be useful for Bradley Fold into Bolton, but is there likely to be much demand from Bolton to Manchester along such a route? I doubt it unless heavily subsidised.
If a means of taking light rail along the main line through Farnworth was worked out, I again doubt that the take up would be worth it. Moses Gate is OK, but Farnworth station is too far from the centre of Farnworth for modern man to walk.
The idea of taking a line from the region of Walkden and using the old track into Great Moor Street sounded a good idea, but again there seems too much housing that has been built over the track, with no clear detour route.
Without much of the route being completely new whichever way one chooses, I can't see a viable way into Bolton that would make building a light rail cost effective.
I like the idea of converting the whole Atherton line from Salford into Wigan Wallgate to light rail, seeing as it's been little more than that for years with all the 'Pacers'.