If somebody offered to install a G1000 in my TB20GT, free, I would decline.
With the mostly nice "early 2000s" separate kit I have, which does everything VFR and IFR ever likely to be needed in Europe with a big VFR/IFR GPS (exceptions: precision coupled GPS approaches when they are available without ATC into GA fields, and RNAV STARs with transitions flown coupled - none of these are exactly pressing and TBH most 3rd world
747s don't have this capability and never will) I can keep my costs to a minimum by sourcing any required replacements from the
USA at a fraction of the UK cost, whereas if I had a G1000 it would be a case of flying the plane to a specialist dealer, with a barrel in the back, putting the barrel in the man's office, and bending over it without him even asking me to.
Avionics integration yields a pretty cockpit but I bet you it will increase operating costs through a severe restriction of maintenance options.
Extra mission capability = 0.