You can use any keyboard and any trackpad.
- Yes, but you can’t buy any keyboard that uses the smart connector, which is probably proprietary.
- And, you can’t buy any pencil that has the proprietary Apple chip to reduce latency and other smart features on the iPad screen.
- And, my guess is that Apple will develop some proprietary features only available on their iPad trackpad.
Like I said, well before there was an ASK or an Apple Pencil, there were BT keyboards and stylus that worked with iPad. Apple held some proprietary features for their accessories alone, so they could up sell their iPad customers. I suspect the same will happen with the iPad Trackpad, and we will see it in the Fall with the public release of iPadOS.