I travelled on the DMU shuttle too. I still have a commemerative ticket for it somewhere. A temporary platform was erected at Mantle Lane for open days because Coalville Station proper had been demolished by then.It is stone freight now, and mainly single line however the odd rail tour has used it over the years and in the halcyon days of the Coalville Mantle lane depot open weekends in the mid 80s, there was even a first gen DMU shuttle that was run up and down the line from Leicester via Coalville and on to Burton, which i sampled at the time.
The first part of the Ivanhoe line from Leicester to Loughborough has been in use since the early 90s now stopping at new re opened stations at Syston, Sileby and Barrow on Soar, but the second section from Leicester to Burton via Coalville and Ashby has never gone further than feasibility studies. I believe that there is a lot of mining subsidence in places preventing moderate speed passenger operations not to mention the track and signal upgrades required
The mining subsidence has largely been remedied now. It used to be quite spectacular at times, the P/Way gangs at Derby and Burton used to operate a 'fire brigade' system of attendance - 'Everybody to Coalville quick, the tracks gone again!'
The only two places on the line likely to generate any passenger traffic today would be Coalville and Ashby, the line isn't really convenient for the other places en route which are quite small anyway. The missing curve at Knighton isn't insurmountable but as you say, the track upgrades would be cost prohibitive. I don't think it's ever likely to happen.