I think regardless of implementation, if the added complexity reduces reliability and introduces forced failure modes it's reasonable for people to avoid these systems altogether. For example, EGRs causing fouling or DEF engine throttling.
This may be true for our group, but I know numerous blue collar workers at the poverty line struggling due to these systems. Corporations / manufacturers have no incentive to make these systems more accessible. Even if they did, more complex -> more expensive to repair.
> Corporations / manufacturers have no incentive to make these systems more accessible
That's the exact point of actual right to repair legislation.
> Even if they did, more complex -> more expensive to repair.
No, this is not true as a general rule. For example if problems can be diagnosed easier (or even ahead of full failure) with digital controls, this brings down the cost of maintenance. Or if the hardware shrinks in complexity while the software grows in complexity more, this can still be a win as individual bits of a digital controller aren't likely to break down.
But on this topic we aren't actually talking about manufacturers being able to resume production of the previous non-digital engines. This would require actually repealing the Clean Air Act, and probably even directly mandating that manufacturers remove such systems from their current designs.
Rather the only thing this declaration seemingly does is remove one excuse manufacturers have for having locked down their systems with digital restrictions, with the goal of allowing customers to "disable" those extra controls "temporarily" - not really an actual win for any of the repairability or cost issues you bring up.
This is the same fundamental dynamic I've observed in all of the destructionist policies - large print that performatively throws a bone to those suffering, but the actual details don't even try to unwind the poor dynamic - never mind attempting constructive solutions (in this case, straightforward right to repair legislation).