Making new designs of anything comes with added environmental impacts, versus manufacturing more of the same.
Adding electronics to vehicles clearly reduced tailpipe emissions. But "electronics", probably more so than any other vehicle aspect, comes with its own hefty impact which I think has been completely ignored over time. That industry, and all the industries required to support it, are huge. (For brevity below, I will use the word "energy" but also mean that its consumption often incurs pollution.)
I imagine all the raw elements required to make the thousands of electronic components in a modern vehicle's power-train and emission system, times millions of vehicles. Producing those raw elements requires energy. They also require global transportation and processing, each step drawing energy along the way, if not causing environmental harm themselves or through their processing. And of course the component manufacturing and global transportation and storage takes energy.
I think of the millions of people who commute to work every step along the way to make these parts (and software!), and their impact. What about all the efforts to sell and market these parts? 'Every brochure, website, email, spam, catalog, seminar, exhibition and corporate classroom...
And once in the new vehicle design, all of the components draw electrical power, for the life of the vehicle. (And they and their wiring have mass which is carted around, meaning slightly lower fuel efficiency, for the life of the vehicle.)
As the vehicle ages, its complexity makes it more difficult to troubleshoot and repair (man, do I have stories)--and more expensive to do so. And these expenses make a vehicle more likely to NOT be repaired and junked instead.
Also, in our state, we have to drive each vehicle to have its emissions tested, too. (And the requisite paperwork, mailings, staffed testing centers where the employees drove in, each building using its own energy, etc.)
I'm just saying there's more than the tailpipe to consider and I don't think anyone has.