Apple doesn't need to support its own trackpad because as of iOS 9 trackpad functionality is already built in the iOS system software.
So far, other than Bluetooth keyboards, Apple does not, and appears, will not support external mice or trackpad input devices.
Apple, at any time, could have put this functionality into any iOS version to date. Apple has chosen not to do so.
iOS 10 STILL does not support external wireless Bluetooth mice or trackpads.
If you do not like this fact, you have other alernative tablet hardware and tablet OSes.
No one here is going to change the fact Apple does what it wants to do.
If Apple does not want users to use external mice or trackpads with their touchscreen mobile computing products, then that what Apple is going to do.
Accept this or move to another tablet device that will have this functionality.
I use my iPad Pro in a creative, but professional manner and I do not feel any need for ANY external input device at all.
Since day one the in 2010 when the iPad debuts, I have trained myself to use (and use very well) the iPad's iOS software keyboard and the new trackpad feature of iOS 9.
Many users are simply lazy and want familiar tools (crutches?) to use with a device that has been designed to negate using such bulky, cumbersome external input tools.
Apple, it seems to date, is not budging on giving users the ability to use external mice or trackpads.
Apple is not going to change its policy on this matter.
Not as long as they are still manufacturing and selling laptops that have the functionality you are looking for.
iPads will get closer to being a laptop replacement, but as long as Apple is still producing and selling laptops, iPads will never fully reach this status.