IMO it's problems are that it's "noticable" to the luxo cruiser drivers whose cars it has ended up in and "unnoticable" in the EPA gas-brakes-gas-brakes test scheme. Anyone prepared to put up with a minor stumble as it switches in and out, and who will drive at steady highway speeds would benefit from it... NVH scores more than MPG... even in economy cars... look at all the 3cyl and 4 cyl motors that got inertia hogging, HP losing balance shafts, look at the "silencer" in the 2nd gen ford escorts airbox... there are numerous examples...

I shall :p
Getting a good baseline and testing emergency aero mods 1st though. One guy with a minivan same as mine reckons it's good for 35-40mpg on the highway...

IIRC the primary reason for closing valves on deactivated cylinders is so that you are not pumping an excessively lean mixture into the catalytic converter
Satisfy my curiosity on this issue when you are doing injector-kill tests and measure catalytic converter temps with a noncontact thermometer. I would expect the temps to be much higher if youre pumping all that extra oxygen downstream. the only way I could think of getting around it is to have a separate exhaust system for your deactivated cylinders in lieu of disabling valves

That's a possible, might find one of those cutouts if I have issues.

Dodge 5.7 cylinder deactivation
 

Just had a valve drop into the piston braking the rod and stabbing a hole in the block. After taking some time reading this post I thought I would give it a go. Here's what I found, I removed the oil pan and found some parts so thinking about it I noticed deep scratches on the cylinder wall and a stuck piston, it's destroyed right? Wrong wrong wrong. I cut the stub or the smashes rod off and left the rod in place. Then cleaning old pan up and patching the hole in the block with job weld "size of a fist". Then removing passenger valve cover and removing spring and clips from the dropped valve. Then removing both Rockers and push rods on the damaged cylinder. Again plugging the exhaust valve hole with job weld seeing how now that the valve is into the piston. And I left the intake valve alone seeming show it's not going to move anymore. Put the valve cover back on.Next step unplugging injector and coil for the damage cylinder but leaving coil in place to give the stock look. Filled the finely tuned motor with new oil and starting it. Now having more than 5000 miles on it, it's still running just fine and only a very trained ear could notice a slight miss, seeing I have after market muffler it gives it a rumble and sounds good. As for power it's not really noticeable unless you tow a trailer but it has always been doggy. That's my two cents. I have about 40$ into oil filter, oil, and ten tubes of job weld. In short it works and it's a seven cylinder and I did not notice any gas savings or more gas uses it is almost the same.

Best engine repair story, ever.