There may be a weight limit for an IFS, but it's well outside of what our coaches may need. Mine is 14,600 and I know of another that is 16,600.
It's probably cheaper to swap coaches than tear out the entire front end and replace. Remember, it's the steering mechanism as well as the suspension. All for very little gain, in my opinion. I'm not knocking IFS (afterall, I do have one), but don't expect any dramatic difference in ride or handling.
Per the Freightliner website, your 2006 Discovery has a 12,000 lb front axle, probably a Neway I-beam axle. Freightliner typically uses a ZF brand IFS, but I've never heard of one being installed in an XC-S chassis. Doesn't mean it can't be done, of course.
