I've been mulling over this project for about a month. I started out thinking just a small shelf at the back, enough to cover the gap behind the machines; then maybe a false back to hide everything. I'd also considered a counter-top - I didn't look into that a lot, so I'm not sure what would be required to "float" one over the machines; but there is not a wall available to support it on the right-side and I'd still have to deal with the connections at the back. There is already a small counter-top (you can just see the top of the back-splash next to the dryer), with a base cabinet and sink, so we'd have two different counter-tops right next to each other.
I also realize these won't last forever and their size may change - this is a brand-new pair that just replaced our 20-year old Maytag pair (the washer completely fried). It's crazy how much larger the capacity has become. But we have a 7-year warranty on this set, and I'd like to think we can at least get ten years out of them. It's hard to say what the machines will look like by then.
Actually you do need to access the plumbing often. I do work for a company that does fire and flood restoration and you would be surprised how many houses are flooded by a burst washer hose. I have since got my family to turn the water off after every use.
We have never had an issue in the past, but we also err on the side of caution. The water hoses are the braided stainless steel type, and they have some type of valve inside them that is suppose to shut off the water flow if they detect a burst in the line. We also turn off the water at the shut-off when we're not doing laundry (hard to tell in the picture, but the valve is in the off position).
Having an open back cabinet will allow access to the shut-off and the cords (although I don't see a lot of need for the cords). I plan to hinge the doors conventionally, so you're correct that nothing could be on the machines when we open them, but we don't keep anything on them. We do use them for folding clothes, which is why this whole project has come about. My thought is also that in a worst-case scenario, the entire cabinet can be removed by taking out the six mounting screws.
I'm sorry if I didn't provide some useful information initially, but I didn't want the post to be too long.
So, if I proceed with the cabinet idea, does anyone have any thoughts on my three questions? Thanks to all of you for you input and advice!