I haven't a clue from a technical viewpoint whether it is feasible or cost effective, but I love the Superliners and wish it was possible to modernize them to get many more years out of service. I understand it would be a major overhaul with essentially only the shell remaining, And, they could use more cars because of attrition due to wrecks, not to mention potential growth, so refurishment doesn't solve that problem.To replace the superliners they need to add to the viewliner 2 sleepers and diner order, order a whole bunch of Siemens cars configured with long distance seating, and some sort of lounge car.
I don’t think the European style sleepers will be well received compared to the superliners and viewliner we are used to.
Imho it would be better to start a massive refurbishment program on the superliners where the HVAC and toilets are replaced and the interiors updated. This should apply to all cars. Could get another 30 years out of the f them I bet.