With CSS grid it would be a pretty simple, even small amount of code and allow you to slide the entire menu out of the way and put more cars or trucks on the same row. I can put some code together and show you or even stick a site together, scrape some inventory, and stick it online for you to see.I'm a developer so I love cramming in all the shiny objects and even more shiny objects in the box. Problem is that most people won't use 80% of the features. It's an addiction I fight daily.
I'm a big fan of Steve Jobs mentality of keeping things simple as hell too which helps keep that addiction under control.
So, the left bar slider is probably something I'd stay away from since most people now have 15" monitors or more importantly are on mobile.
I've seen very few sites that actually accommodate mobile. Sure, they are responsive but that doesn't mean they are mobile. Our site is mobile responsive is just a marketing.
Another topic that is hardly covered is the 1 page threshold. I'm going to say that 50-60% of people don't scroll to the second page. So if the CTA is anywhere not at the top and your hero is there, you have lost out.
I am mention ADA compliance a lot. Previous company I worked for created a beautiful design. On the day of the demo, I said it wasn't complaint. The Design Team manager was all butt hurt and said it was. 6 months later, we were redoing the design because it wasn't. Dealers are lucky they are making enough money to be getting emails from lawyers. These lawyers are 1000% ambulance chasers. So,TLDR; I agree with you!
What I'm working on is pure self built. I am a app/web developer by day job but have moved up to management. I'll share with you in a few days after I clean up some of the bugs I found. I had to fire a developer recently so this roll out go delayed.
TikTok proved people will scroll all day and I've clicked through an entire site looking at classic cars, the problem is most dealerships inventory is boring but if you could figure out a way to spice it up with something like a customization app, or something that would add a little excitement to it so your not looking at the same car over and over again.
The ambulance chasers haven't gotten to the dealerships yet but they will, they normally ask for $5,000 not to turn you in but as the government decides they want more money or a competitor decides to hurt a dealership, or manufacturers decided they want to go direct to consumer and get rid of the dealerships, ADA fines start at $50,000.00 per an incident, lawsuits are counted per a visit, per an incident, and no dealership has a website that is ADA compliant.
And why it should be the developer getting sued sadly it all falls on the site owner.