My prediction: Apple will build one Silicon processor that matches available iPhone technology of Dec. 2020, increasing the clock speed to 3.5 Ghz. Then they'll check which current Macs would be significantly improved by this (all dual cores, maybe quad cores, maybe not) and replace the processor.
As soon as possible, Apple will create a processor with twice the number of cores, and again replace the processors where this new chip is a significant improvement. That would be everything with 4 and six cores, possibly eight.
And as soon as possible, Apple will create a processor with four times the number of cores, and again replace the processors where this new chip is a significant improvement. That would be everything with 8 or 12 cores, possibly 16 and 18. All Macs except the highest Mac Pro models.
What next? Either Apple builds another bigger processor or takes existing server designs, like the 80 core Ampere Altra to replace the Mac Pro Intel chips.
Apart from that, no model changes. Apple may continue selling a very small number of Intel models for people who need to run Windows etc. Apple may build 2.5 GHz versions for laptops or possibly a mixed 2.5 / 3.5 GHz version (I don't know how hard this is to do, but it would save power for laptops), and they might create a Mac mini that is at least twice as powerful than the current six core model.
As soon as possible, Apple will create a processor with twice the number of cores, and again replace the processors where this new chip is a significant improvement. That would be everything with 4 and six cores, possibly eight.
And as soon as possible, Apple will create a processor with four times the number of cores, and again replace the processors where this new chip is a significant improvement. That would be everything with 8 or 12 cores, possibly 16 and 18. All Macs except the highest Mac Pro models.
What next? Either Apple builds another bigger processor or takes existing server designs, like the 80 core Ampere Altra to replace the Mac Pro Intel chips.
Apart from that, no model changes. Apple may continue selling a very small number of Intel models for people who need to run Windows etc. Apple may build 2.5 GHz versions for laptops or possibly a mixed 2.5 / 3.5 GHz version (I don't know how hard this is to do, but it would save power for laptops), and they might create a Mac mini that is at least twice as powerful than the current six core model.