OS 9 -> OS X was supported by the Classic runtime for years.
PPC to Intel was supported by Rosetta for years.
I suppose if the announced that this was the plan, and gave people years to migrate across, it might be something they'd do. But it would kill basically any technical use of the platform (development, scientific computing). I find it much more likely they'll evolve iOS "up" to support users for whom a closed appliance approach is helpful, whilst adding options to OS X to cater for those who want a more traditional computer but need a bit more help.
I suppose if the announced that this was the plan, and gave people years to migrate across, it might be something they'd do. But it would kill basically any technical use of the platform (development, scientific computing). I find it much more likely they'll evolve iOS "up" to support users for whom a closed appliance approach is helpful, whilst adding options to OS X to cater for those who want a more traditional computer but need a bit more help.