Multitimbral? What do you mean? Reason IS multitimbral, because you simply use a new instance of a synth when you need a new sound. The synths themself are mono-rimbral for sure, but that keeps programming them easy, and if you need two sounds at once you simply create a new synth.
BTW: native instuments awesome Kontakt works in much the same way: the plug-in is multitimbral, but in fact you create a new (mono-timbral)instrument in the sampler rack everytime you need a new sound.