I currently own a 2012 3.5l Limited but the car I traded in for it was a 2009 Corolla which shared this 2.4l engine (2AZ-FE). I owned it from March 2016 until September 2016. Here are a couple of observations I had about this engine from my experience if this helps:
-I had close to 78,000 when it was traded in for the Rav4. During my short time owning it I went through the same experiences you had. A LOT of run around, a lot of other forums and similar experiences.
-I typically change the oil in my vehicles twice a year, about ~5,000-7,500 miles between or no more than 6 months elapsed between changes and always with synthetic (which right or wrong is always what I have done on my vehicles). Upon changing it out as well as checking the levels during gas fill ups, the oil was always darker and smelled burnt. Several times out of curiosity I opened the oil cap at the same time and smoke would rise out from the block/valve cover. It wasn't a faint smoke nor a thick smoke necessarily, but a clearly obvious burning oil smoke wafting out from under the oil cap.
-In the 5 months I owned this vehicle, I changed the oil twice due to these reasons. Clearly the engine was was burning as well as consuming oil. To be fair I drove it mostly daily in city with two longer extended travel trips. About 6,000 miles total.
I read the literature on Toyota's lack of response over several years, and then finally their reluctant procedure to check it at dealerships. I don't remember at this point what specific amount of oil had to be "lost" between changes in order for them to rebuild the engine but I do remember it is a significant amount , i.e.:
-You typically would have to be burning/losing so much oil that the engine would be at the full mark and have to be below the low mark on the oil dipstick after 30 consecutive days for them to consider further investigation.
-The dearlerships I talked to said Toyota only allowed 2 attempts to show this was the case with your engine. If you got close, like I did after doing the test, that didn't count and you were allowed to try one more time to "prove" your engine was "not at operating standard". If however, like my vehicle, it burned all the oil down to just above the low mark after 30 days that did not count as Toyota considered this "normal wear and driving". Clearly this is NOT normal for any given standard consumer vehicle engine.
-They did this investigation by you starting a complaint. The dealership would take the vehicle and do the oil change for you. They would mark the drain plug, filter, and oil cap with a light colored sealant to make sure you weren't tampering with adding/removing/changing the contents. You were given a set amount of time to drive the vehicle, I believe it was 30 days. At which point, you returned to the same dealership and they would change the oil for you and document the differences.
-If they determined your car was consuming a lot of oil, they would then grant you (I believe) a loaner car and the dealership would go about replacing the piston rings and I believe pistons. Who knows how long they would keep the vehicle for in that case.
From what my nearest dealership told me (and I've had a lot of good experiences with mine) is that carbon builds up on the first piston rings and over time creates wear and or breakdown to the point where oil is then slipping past and burning. Toyota created this final solution to test vehicles and really try to minimize their damage by making it very difficult to fail the test. In this case only the absolute worst offenders where the engine barely goes a few weeks before needing oil added would even be considered to be replaced. And like others noted there was a timeframe as well in how many miles and/or years had passed before you wouldn't be allowed to even ask for the testing to be done. Essentially, Toyota knew there was a big problem with these 2AZ-FE engines from all the complaints across many models and they had used them in several Scion models all the way through some Corollas, Camrys, and the Rav4 (I believe some earlier Highlander models as well). Because of this they replaced this engine with an updated 2.5l engine which is now used in many vehicles including the new Rav4s which don't have this issue.
Like others have noted and it sounds like you know it is a big problem. I personally didn't enjoy the used Corolla I bought anyway so after all these engine issues I gave up and took a big loss to get out of it and into something I wanted rather than drive something that wasn't useful to me and came with a lot of constant maintenance issues. Having said that I think the others are right. If you stay on top of adding oil in every couple of weeks and you're good about maintaining much more regular oil changes then these engines should last you a good long while it's just that they burn a lot of oil. I personally love my V6 Rav4 and it may so far be one of the best vehicles I've ever owned all things considered, so if you feel the same way about your I4 then I would consider keeping it and just putting up with the issue. Other than that I think you will be very hard pressed to get Toyota to do anything about replacing the piston rings and dealing with the excessive oil consumption unless it's bad enough that it will leave you stranded on the side of a road at any week.
Sorry to be wordy, been down this road in a big way. Hope this helps.
