Summary for newcomers on what we know certainly so far;
- MCU2 upgrades are possible if you have Model S with AP2.0 or 2.5 (built after late 2016, with pillar cameras) This is proven by
@verygreen
- For cars with AP1 or later you need harness/pin changes theoretically. No one has tried if they can make it work practically after said harness changes. Just too much work. Not enough is known to say possible/not possible yet.
- To do it with AP2 or later cars, you need to change tuner, MCU and instrument cluster with MCU2 parts. Just drop in replacement.
- After replacement you need to program it so it would work. This is beyond most people as there are very few 3rd parties that can adjust Tesla software for you. Most of which don't have experience with MCU2 rooting. So it leaves you with a handful of people you probably already heard about.
- After the retrofit it works perfectly. However AP2.0 still doesn't get sentry recording as that needs Autopilot Engine replacement. Has nothing to do with MCU. Yet AP2.5 that already has sentry gets additional cameras to be recorded after MCU2 upgrade.
Will Tesla offer it? We don't know/I don't think so. Elon tweeted that it should be possible for 2k (which I find to be a cheap estimation he possibly regrets tweeting)
Also in his said tweet he hinted that it is an
unnecessary thing to do 'just for additional features'. So he played it down. However the changes from MCU1 to MCU2 is nowhere near minor IMHO. I don't think any MCU1 owner dares to pinch/zoom around the nav to discover the area or pin a location manually to navigate to it after v9. It just doesn't render even with prefect LTE speeds. Not even mentioning the laggy UI, lagging sound alerts, crashing or the infamous dead-MCU1 issue.
Tesla doesn't have to offer MCU2 replacement as long as they can deliver FSD to AP2.0 with MCU1. However as of today the way to retrofit HW2 cars with HW3 is blocked due to camera color filter differences between HW2 and HW2.5. Would software make a HW2/MCU1/APE3 setup possible? We will see. I just don't feel like this is a priority within Tesla at the moment and I think it should be. Early adaptors are being left in the dust for deliveries of the 3, development of the Y etc. I guess this is how businesses work. We got caught up in Tesla too much maybe? If I were in Elon's shoes instead of messing with hardware changes that would clog up service centers for minor revenue, I'd assign a team to make MCU1 cars perform like V8 and earlier with further software updates. That might cost some features but it is expected that newer cars have newer features. What Tesla is doing today is looking like adding new features to MCU1 cars while making older features' performance so bad (browser) that it renders them unavailable, while not being able to add those new features either.
p.s. After proofreading my post I had a laugh remembering Elon's
'war against Acronyms' leaked e-mail a few years back. Look where we are now with abbreviations. Here's the dictionary;
MCU: Media Control Unit (central touch screen)
APE: Autopilot engine. Above the glovebox with all Autopilot 2+ cars. Super computer responsible for driver assist features.
HW1/2/2.5: Hardware of Autopilot. Actual autopilot hardware consisting of cameras, radar and ultrasonic sensors.
HW1: Autopilot 1 cars' hardware. 1 front facing radar, 1 front facing camera and ultrasonic parking sensors.
HW2: Autopilot 2 hardware. 8 cameras, 1 radar, ultrasonic sensors, APE2
HW2.5: Autopilot 2.5 hardware. 8 cameras with different color filter, 1 radar, ultrasonic sensors, APE2.5
HW3: Autopilot 3 hardware. 8 cameras with hw2.5 color filter, 1 radar, ultrasonic sensors, APE3
. I may have missed that tweet. 
