Well, that's understandable. Parts availability for the MCU2 I would guess impedes doing both. Getting both done at the same time is certainly convenient. I am glad that I was able to do both. I see reports of some people getting AP3 engine, but not interested/not installing MCU2. I hope it works for them, but others are reporting they don't maximize the same features such as visualizations with only MCU1.
The upgrade from MCU1 to MCU2 for me was worth more than just visualizations, more than just AP3 too. Don't get me wrong. AP3/FSD is going to be fun. But staving off the issues of an eventual failing of an eMMC, even under warranty, doubling or tripling of the time before a MCU2 eMMC would fail is singly, to me as valuable as AP3 or FSD. The performance of the new eMMC is great. My '17 S behaves like a new car. I am very pleased with it.
Then besides those things already mentioned, there's Sentry and Teslacam and Tesla Theater. I already had two dashcams, so I was not dependent on Teslacam. But you can't have too much security so its a nice addition. Nice addition in a different way than my own dashcams so Teslacam and Sentry were a help.