Are these changes needed? In my previous posts I was subtlety hinting that the design and documentation process we use in Canada could be adopted in some way in the US and that it might help lower your costs - smaller fan, decreased noise complaints, reduced call-backs, more referrals, added value etc. Adding the design and documentation components could be included starting tomorrow in the next mitigations that you perform and in a short while you might be able to see this added value pay you back real quick.
Frankly, discharging at the rim joist is not all that advantageous and is the less interesting aspect of the Canadian approach and is something that probably should not be considered without also taking the design and documentation and sealing approaches first.
Why? Well for one thing, having your fan outside and exhausted above the roof helps to hide the big noise footprint of using more powerful fans. When you take the "super-sucker 4000" fan and mount it inside the house you are asking for trouble. When the house is real quiet at 2am and that 100watt fan that seems not too loud during the day suddenly becomes intolerable at night - you will hear back from the customer - then what do you do? Install a smaller fan and retest? Isn't that backwards? Also, when that exhaust noise that you have been pointing up and into the stars suddenly gets pointed at the neighbor's house or in the backyard, it can also be too noisy. Mufflers help to take the edge off but they are not magic.
I'm not sure which came first the chicken or the egg - in this case but I feel that the design process that predicts the correct amount of negative pressure for each particular house goes hand in hand with the ability to install a fan indoors and the exhaust at ground level because the process helps to ensure that the smallest fan that can be shown to work is used from the start.
Along with this is also our guidance which says that we must seal "all accessible leaks". This is close to pure magic. I have fixed many homes that would require the "super sucker 400" only to allow me to use a 20 watt fan after a thorough sealing effort (which can take 30% of the time onsite). Sucking from a perfectly sealed container takes almost no fan power while sucking on a leaky container sometimes isn't even achievable with large fans.
Finally, exhausting at ground level has you competing for precious wall space. We have clearances to other openings, mechanical air intakes, corners, gas regulators, windows, and everything else that poking through the mechanical room wall. Often, we would have to first go into a garage or adjoining room to get the clearances we need and this can get real tricky. Or we're moving other ductwork that's in our way. Just poking through the wall anywhere and pointing up to the roof sounds like the easier approach in many instances.
My advice is to start with the design and documentation. Add this value which will get your profits up and reduce costs. Get used to spending a lot of effort sealing. Reduce callbacks. Start using small fans when appropriate (we are 96% 20 watt fans regardless of building size or soil material) and get the noise footprint down. When all that is second nature - go ahead and drop the exhaust to the ground - re-entrainment is almost a unicorn. But I think you will find the unintended (mainly noise) consequences of starting with ground level discharge to be not worth it if you don't do the other first.