You would not say you need "special" steppers, drivers. power supply etc for plasma VS router.
You do need to understand:
The Physics of the two types of cutting are a lot different
Plasma cutting requires high speed (150 to 300 IPM on some material) with acceleration at the higher speeds. Acceleration comes from one of two sources: More torque (bigger motors, belt reduction, etc) OR less weight on the gantry. That can be contrary to router cutting because a lighter gantry may tend to flex more given the lateral forces of milling and routing. In short you may have to build a heavier gantry and upsize the motors to do both jobs effectively. That may force other componets to have to be upsized.
That does not mean it won't work with lighter duty components; just that it may not give optimum results on one or both processes. You might not be able to cut thinner metal and get sharp turns or square corners. You might not be able to chuck in a 1/2" mortise bit and cut dados in hardwood in one pass.
A plasma/.router table is a compromise. Sorta like a Sports/Dumptruck. You either have to overbuild it to do both types of cutting or live with the compromises
You also need to consider the other factors:
Fire & sawdust (need I say more?)
Plasma smoke and dust
Water Tray and sawdust
Setup time to get a flat cutting surface for the routing
A lot of it has to do the type routing and the type plasma cutting you will be doing. To cut thinner material you need a table that can cut at up to 300 IPM and have enough acceleration to get there quickly and you need lower speeds and more torque to cut with a full sized router and cut denser materials.
The plasma process needs more attention to noise immunity but a well designed control system should already have that.
Cutting metal with a 30.000 degree flame vaporizes a lot of it and blowing it out of the cut with 70 PSI of air tends to generate a lot of nasty smoke not to mention hot smoking pieces falling off under the tabler. The type smoke and flame suppression for plasma is a lot different that a dust extractor at the cutting bit.
For a shop super limited on space and that does not mind the downtime between the change over and that cleans the table completely after a job a combo table can be fun to run and highly flexible. For a shop that is looking to make money with one or the other process I don't recommend it.
So to clarify. You can build a pretty good table to do both and if you can live with the downside your electronics can work for both. If you want the BEST (optimum) for each type of cutting you will be forced to upsize some components and perhaps move to a servo system that offers a wider range of torque/resolution and speeds.