add user interrupts on future device

As I know,all MCUs design interrupts for only internal peripherals.It occured to me that I can use it to drive 'tasks'.
We usually write our embeded application programs based on an embeded OS.I get to know it is ok to drive a 'task' by an interrupt especially in some little applications.
To do so,we really get a OS which is drived by hardware. Schedule time is 0,and context switch time is in deed as a very fast interrupt entrance.
But,in other hand,we have to change our program models,which have been used with an embeded OS.
To make it come true,we should first get a MCU with some user interrupts.Or,we can only use some available interrupts belongs to internal peripherals as those user interrupts.
It's only an idea.I havn't do any experiments.
Does anybody interested in this subject?
Thanks,