It depends how do you define outdated – in terms of functionality or sensor quality. I owned Canon 550D, later on I switched to full frame Canon 6D. I still kept 550D as a backup camera. Later on I replaced 550D by newer APS-C model Canon 760D (old sensor 18MP, new – 24 MP). I was amazed by how much sensors improved in APS-C models. Image quality at high ISO setting is pretty much on par with full frame 6D. I place more value on sensor quality. So, for the switching point is the new type of sensor.