Given Apple's track record of supporting older Mac hardware, I would expect Intel Mac hardware to be supported for many years and many OS versions after the last Intel Mac has been produced.
Also given Apple's recent MacBook track record, the first version of ARM Macs may not be as much of a slam dunk as people hope.
Which track record are you talking about? Apple discontinued OS support for PPC only 3 years after intel was announced. That means no more support for xcode and new commandline tools after 3.5 years.
Also given Apple's recent MacBook track record, the first version of ARM Macs may not be as much of a slam dunk as people hope.