I’m amazed at how many people equate the mini jack to other “legacy” ports. The mini jack long predates scsi, 5 ¼ inch floppies etc. It’s also not a computer port. It’s a universal connector, which will continue to be used as an audio out for decades to come (yes, really). In other words, it’s not the same. It’s more akin to Apple suddenly deciding they were getting rid of the qwerty keyboard. Which of course may happen at some point...
I use my iPad Pro for presentations which require good sound (I’m a senior Music examiner and I’m using it for examiner training: I connect them to a pair of high quality active monitors). So I really do use it for a purpose for which otherwise I’d buy a cheap laptop (windows) with an audio out port. There’s no logic to it’s removal. I’m not that worried though, because while I can imagine Apple doing this, I really can’t see them moving the keyboard or iPad to portrait only, so I’m assuming the whole thing is rubbish.
Your usage case is valid and you do objectively benefit from having such a port, no doubt there. However, you are in a small minority and for most people, this space will most likely be utilized better (for example, by putting a bigger battery). This port is quite large, when you think about it.
However, even for you, there is a solution which includes a very cheap lightning adapter. And if you need to charge the iPad at the same time, you can use a charging stand with the smart connector, or an adapter that supports both pass-through power and an audio port. I agree, this is not a better solution for you, but when you think about it, you have a (relatively) small trade-off, while the majority has benefits.
And I agree, not every change benefits everyone, especially people with specific needs. For example, I could really, really use a 15" or even 16" iPad Pro for illustration (heck, I could go for a 21" too), but I know this iPad would sell poorly and I understand why Apple won't make it. One day they may decide to stop making a 12.9" one in favor of a smaller one - I would be sorely disappointed, but I would understand that they do go for the needs of the many, not the needs of the few - to paraphrase Spock
You don't have to agree with this decision - in fact, you should be vocal about it if you dislike this (possible) change. This stands for everyone here criticizing this potential removal. Say you prefer the headphone jack, by all means. What I don't get is people acting like there is no good reason for Apple to do so. There
is a good reason - and you have full right (and in your case, a good reason) not to like it.