When someone says 4 slot TRBO system...I immediately think of how Capacity Plus counts channels. Repeater 1, TS 1, TS 2. Repeater 2, TS 3, TS 4. Repeater 3, TS 5, TS 6...
So technically Motorola already has it...a 4 slot system is just a two channel Capacity Plus system. Want to put it in 25 kHz of spectrum? Let's pull a Kenwood (with NXDN dual 6.25 kHz channels in a common 12.5 kHz) and say we can do that...just need two Repeaters and a hybrid combiner.