On the subject of controlling endorsements at multiple units, many moons ago at RAF Linton on Ouse, I held 14 of the available 18 endorsements as the Unit operated 4 aerodromes: Linton, Topcliffe, Dishforth and Church Fenton. My Blue Book had Linton Tower, Ground, Talkdown (PAR and SRA), Departures and Zone; Church Fenton Tower, Ground, PAR and Approach/Director; and Topcliffe Tower, Ground, Approach/Director and SRA (on ACR 430). The only ones I didn't have were Linton Approach, Director and Supervisor, and Dishforth Tower.
I had no bother staying current as there was plenty of traffic but most of that traffic was Tucanos and Fireflies flying academic training sorties, so there was little variety other than the swarms of gliders and GA that used to monster Fenton Approach.
I do not like the sound of controllers being expected to control different remote towers simultaneously at all, so I see little saving in manpower terms, but I see no reason why they could not control different towers from the same location at different times within the limit of their licences. Imagine a tower controller operating in the Scottish Highlands; he/she could control both ends of all the short island-hops in sequence from, say, Prestwick. The savings will come in reducing the required infrastructure at aerodromes.
Once they sort out the bandwidth and display issues, I could work from home!