@whitex -- while I am 100% behind you on the chance (i.e. asymptotically approaching 0%) of an MCU retrofit program being done, I'm told by a very reliable source that Tesla already has an MCU2 retrofit kit/harness designed and built internally. It wouldn't be an MCU 1.9, it would be a retrofitted MCU2. They could mass-manufacture it and offer an upgrade path. But at this point in time, they have shelved it. And the longer time goes on, the less and less likely they'll ever release it.
Even if you are right and they designed a retrofit kit/harness, unless it literally replaces EVERYTHING that has to do with the new MCU2, adds the new antennas, new instrument cluster,etc, bringing it 100% identical to factory MCU2 car, it would still be not be an MCU2 configuration. To illustrate, let me give you an example: MCU1 has single 2.4GHz WiFi band, MCU2 has dual band 2.4/5GHz. If this new retrofited MCU2 doesn't have a matching antenna in the side mirror, but the software doesn't distinguish between actual original MCU2 and retrofited MCU2, then the software will enable both bands, but 5GHz will function horribly it at all without an antenna. So, your car sees an AP, connects 2.4GHz, AP is informed the car has dual band radio, AP has band-steering enabled, it sees a very strong 2.4GHz signal, so it terminates the 2.4GHz connection reasoning that the car will reconnect on 5GHz. The car tries, fails, so it reconnects back on 2.4GHz and the whole cycle repeats - the car is stuck in infinite reconnect loop. If you tell me that the software will somehow know that it's running on a retrofitted MCU2 as opposed to factory MCU2, then you are telling me it's a new configuration, which you'd call "retrofitted MCU2" and I just dubbed "MCU1.9" - a new configuration for software to account for, be tested and maintained. WiFi is not the only difference btw, there is also integrated vs independent instrument cluster, bluetooh, etc.
Then there is training of all service centers how to install such retrofit, and then amend all repair manuals to account for such retrofitted car - yet another configuration to support. Oh, and then yet another part (retrofit kit) to keep for repairs and for sale in the parts supply chain (which we know is already giving Tesla plenty of troubles scaling).
So, we both agree it's not going to happen, I can just think of many more reasons why not.