Many thanks for the contributions!
So, the actual L-1011 has similar or cheaper operating costs than actual competition, with better features such as noise emissions, passenger comfort (this is always subjective, but assuming lesser noise, combined with the increased stability from the Active control systems, equals to better comfort) and flying characteristics that are a no match for any of these days aircraft, even the speed, only the 777 can reach the cruise speed of the Tristar.
So, with all these features which still are ahead or in-line with current competition, we can assume if we would change the engines using modern ones, with improved efficiency, less emissions and noise, replace the commands for a fly-by-wire system and using new glass cockpit navigation avionics, we would have a strong (very strong) option in the long range aviation market, without any doubt!
This kind of upgrade was made by both Boeing and Airbus, with their Neos and Maxs!
It could be a very lucrative move for Lockheeed I think, having still the production facilities, so they can produce the aircraft, with a relative small amount of investment, they can place in the market an incredibly saleable machine.
And afterwards, perhaps move to create a new civil aircraft design using all the knowledge gained in the military. (But that's another story!)