> more powerful that the PowerPC systems of MorphOS, hell yes!

1.6 GHz Ultra 45 is faster than 2.7 GHz PowerMac G5?

> Moving to MIPS brings a lot of benefits that ARM doesn't have

One advantage of MIPS over ARMv7+ I can think of is big endian byte order for both code and data, unless it's a pure little endian MIPS implementation (like e.g. XBurst, Loongson, BCM47xx).