I know, I explained why it is probably not going to change anytime soon (unless the hypothetical scenario above would come true) and @jovirkku also confirmed that it still isn’t possible to do what you want to do. I wasn’t talking about Android apps - Signal, Telegram, Whatsapp, Matrix, etc are all messaging protocols that could theoretically be integrated into the Messages app, which would greatly increase the need for an easier way to share pictures from inside the Messages app and in turn push Jolla to improve the UI with an easy ‘Select picture’ button, but I’m quite sure Jolla is not going to invest resources into improving the Messages UI for a function almost none of their current users/customers would make use of.
People who don’t use MMS will never use it because their providers require them to pay extra for each MMS individually. For example, sending pictures via MMS costs me €0,12 extra per MMS. It doesn’t cost me anything extra to send them via Signal (using Whisperfish), email, etc. How did we do it in the old days, you might ask, when mobile data was still extremely slow, limited and expensive? Simple: we didn’t.
I completely agree that it should be easier and the current way of sending a picture with the Messages app is obtuse, but realistically it’s probably only going to change if enough future US customers (where MMS is apparently used very often) complain about it.