Perhaps you need to read my post again, I never said anything about running an open loop with an O2 sensor.
If an open loop system has an O2 sensor then it's not open loop anymore.
Like I said before, longevity with an O2 sensor is being extended in 2-stroke environments by using an air oil separator.
Unless your bung extender had an air oil separator, I wouldn't expect it to last very long either.
You can't just weld a bung on your exhaust and expect the O2 sensor to last forever...but advancements in O2 tech are going to change that in the near future.

The point I was trying to make that you seemed to have missed was that most EFI quads are open loop and have never used an O2 sensor during their entire existence.
So the fact that an O2 sensor won't work well in a 2-stroke environment is overshadowed by the fact that EFI quads are being run without them on a daily basis.
I've got an open loop EFI setup on my LTR right now, and I can promise you there is no O2 sensor on it.

What people don't understand about open and closed loop systems is that they think an open loop is no better than a carb is at metering fuel for varying atmospheric conditions.
An open loop system can go from sea level at 70deg or 9,000ft at 20deg and KNOW the difference between them.
A carb isn't able to discern the difference, which is why everyone has slightly different jets in their carbs depending on all sorts of factors.
Open loop systems can determine air density from their sensors just as well as closed loop systems can.
Both systems have to be told what to do at those conditions with the fuel map, so they're only as accurate as the tune they receive.
The difference being that a closed loop system can double check to be sure the tune is in keeping with how you expect the A/F ratio to react to that portion of the fuel map.
There's a certain amount of adjustment leeway that you can give a closed loop system to correct on its own, but give it too much leeway with a poor fuel map and it'll hunt the A/F ratio without ever getting it nailed down.
Basically, the closed loop system is only there to accommodate the variables that can't be accounted for with standard sensors.
Things like an injector that's performing a little sloppy, or an ignition coil that's getting weak, running it in densely forested areas (slightly higher O2 saturation) vs. a desert, weak reeds, weak piston rings that lower compression, etc.
Those are things that you can't program into a fuel map, but the O2 sensor will catch.
We're not talking about a whole lot of change here though, it's just not running at an optimal level at all times without the O2 sensor giving it some feedback.

Tuning an open loop EFI is just like tuning a carb, only with a different medium.
If you run a certain set of jets and needle position for winter riding, then run a different set of jets during the summer, then another set for riding in a different area, you still have to tune for each of them.
If you were to take all of your tuning notes (writing down main jet, idle jet, needle position, etc. etc.) in a notebook, you could simply refer to that notebook to rejet for winter, or wherever.
With an EFI, you tune the fuel map with the conditions you're presently seeing and it remembers your tuning.
Come back to it a few months later when the temps have changed and tune it again (just like you would with a carb) and it remembers that tune as well as your previous tune.
Go to your favorite riding spot which has a 2,00ft elevation change and do some tuning there (just like you would with a carb) and it remembers that tune as well as the other two.
Pretty soon, you're going to have a lot of tuning info that the EFI can choose from depending on what the sensors are telling it.
If you're at home, and the density altitude changes drastically enough to mimic the riding spot that's 2,000ft above you, the sensors will detect the density change and adjust tuning as needed.
You may not have every tune for every situation, but you'll be able to see a trend in how the fuel map changes as pressure and temp changes, and smooth the map out.
It may not run great when you get between the points that you've mapped, but it'll be close enough that you won't spend very much time mapping from scratch, only some small adjustments here and there to detail the map even further.
So what you're basically doing with the EFI fuel map is jotting down all of your tuning notes into one computer that doesn't wait for you to say "Hey it's winter, maybe we should up the main jet a size" it just automatically does it for you as soon as those conditions are met.

Here's one reason why I want to see someone install an EFI on an LT....a fuel map is downloadable.
If someone went through all the trouble of tuning their LT and getting it down perfectly, they can email that file to the next guy who wants to try it.
It'll be off, of course, but you'll have a generic base map to start with and fine tune to your bike, lessening some of the time it takes tuning from scratch.
If enough guys get together and start a little database of base maps grouped by different engine mods (like bone stock engine, stock with FMF pipe, stock with Q pipe, etc.), then the tuning time is cut down even more.
People can find a fuel map that was made for a bike with the same mods and have a much better chance at success the first time around.
Fuel mapping for density altitude extremes (like really high altitudes or extreme cold) that most guys normally will never see could be tuned by someone who lives in Colorado or an ice racer in NY to fill in the edges of the fuel map for those of us who will likely never see those conditions to map ourselves.
It's more of a pipe dream than anything, seeing as how there's so few of us LT owners out there, and an even smaller group that might be interested in EFI, and an even smaller group that would be good at tuning an EFI, and an even smaller group that decided to run a particular ECU...you get the idea.
That would be pretty sweet though, a big database of fuel maps that you could pick and choose from, tweak it a bit here and there, and you've got an EFI that's tuned for all sorts of conditions that you'd probably never get a chance to see.