Future-proofing puts you on the wrong side of Moore's Law. Let's say 4G requires 10x the transistors of 3G. In reality that's not a problem because 4G came out 10 years after 3G so transistor costs came down 10x or more. But if you wanted to build a 4G-upgradeable radio years early you'd have to pay for that 10x performance upfront using older and more expensive technology. This same argument applies to future-proofing other tech like video codecs as well.