Yes, I do have plans to switch to ESP32 at some point. The ample GPIOs won’t make a huge difference because we will always need to have expanders, therefore how much GPIO the main controller has is irrlevant as the expanders cannot use GPIO pins from the main controller. The extra GPIOs do help with enabling more sensors especially analog sensors.
ESP8266 also has versions with external antenna plug (ESP-07S).
We haven’t moved to use ESP32 mainly because it takes time to develop, test, and get familiar with a new microcontroller. With ESP8266 we are familiar with it, know the quirks. Also, since the firmware files for both have extension name .bin once we switch to ESP32, there needs to be a good way to make sure users download the correct firmware (i.e. they need to know whether they should download the one for ESP8266 or ESP32, since the files have the same extension name). This is rather difficult to make sure as uploading the wrong firmware can jail the controller.
Regarding expander: NO, you can NOT use a AC expander attached to a DC controller. It won’t cause any hardware damage but you will find that zones on AC expander can only turn on but not turn off. This is because of the way AC transistors work.
There are ways to make a universal expander that works with both AC and DC. That is by using solid state relays (SSRs). But solid state relays are significantly more expensive than traics or MOSFETs, I mean the price difference is in the range of 20 to 100 times. I don’t think it makes economic sense to go with that option.