1) Will iMacs continue to avoid the M1 so that it can keep discrete graphics? Meaning that the recent 27" revision is what to get instead of waiting. 2) Will Apple make the M1 work with discrete graphics in the future and that additional process is why there is a delay placing M1 in higher end devices? Meaning it's better to wait and get an M1 iMac. 3) Will Apple wait until a future M2 or M3 chip which improves the built-in graphics further so that it can compete with current discrete graphics card offerings in the iMac?
1 & 2) No, I think they are using the current M1 lineup as a test bed to mature Big Sur in the real world on the most "simple" machines (no dGPU) with the greatest thermal constraints, power consumption concerns and actual internal realestate. This allows for optimisation on the lowest common denominator hardware.
I don't Apple will follow the convention of what we have previously called dGPU, I think they will keep the graphics processor internal to the M1 chip and in machines like the iMac, with mains power, less thermal constraints and more mainboard realestate they will just scale up the core count, power consumption and clock speed of the compute and graphics components of the M1* chip to give dGPU-like performance.
I would absolutely wait for the M1* iMac and if you have to wait 6+ months for it it just means when you switch over you'll have more optimised and mature software waiting for you when you do.
3. This is at most a 2 year transition and I doubt second or third gen M chips figure into that short time line. I would guess that at least all their portable and iMac computers will have some variant of M1. I think the last machines to transition will be the Mac Pro as they have the most complexity.
Consumers expect the Mac Pro to have graphical power which is not likely to be attainable on-chip and they also expect amounts of RAM which at current density make it unlikely they will fit this on chip or package and they also expect RAM upgradeability. Given Apple have come this far in their vertical integration, it does not make sense that they would rely on a third party for a add-on graphics card which will likely be in the new Mac Pro. I think they will want to produce these themselves. Why free yourself from the shackles of Intel to still be beholden to AMD or (god forbid) Nvidia?