The use of GM350s as a repeater setup isn't something new, Motorola themselves boxed two GM350s into a rack case and called it the TR5000 (other form factors were available). The GM350s have also proved themselves when in service as GB7EB, operating at high power for years without fault. In fact the ex GB7EB TX radio is now used by MB6ILO still servicing the repeater group well, all be it on lower power.
While the "BK" repeater will be able to be used as a backup most of the groups repeaters it will not be able to be used as a backup of GB7TX for technical reasons. We hope this answers the question. It also can't be used as a backup to GB3LO either (before anyone asks!).