I beg to disagree with your reply above.
1.- There is definitely a bug in the D. & D. activity, which can be easily fixed by that small change: in the D. & D. library css file for the .h5p-dragquestion .h5p-draggable elements, remove the text-align: center rule. And removing that rule will not break existing D. & D. activity instances as I'm hoping to demonstrate.
2.- When entering the text editor in H5P activities text is left-aligned by default (the Align Left button is selected by default). Users who want their text to be either centered or right-aligned need to click the relevant buttons on the toolbar. Unfortunately, because of the bug mentioned above, the text-align: center rule over-rides the align-left default behaviour of text. On the figure below, I have attached to a D. & D. display the extract from the content.json file for each draggable item.
As we can see, the draggable text which says "left-aligned (default) text" does not have a style rule, it's not needed because left alignment is the default behaviour. I have created 3 text draggables, and, as per the bug, the text which says "left-aligned (default) text" is displayed as centered.
3.- Now let's see what happens after simply removing the text-align: center rule from the D. & D. library css file for the .h5p-dragquestion .h5p-draggable elements.
The draggable text which the user had originally selected to be centered is still centered, ditto with the right-aligned text, and the default left-aligned text is indeed correctly displayed as left-aligned. Everybody is happy.
What you wrote "... removing that property would allow to change the positioning, but all existing content would automatically use left alignment" is not true.
Actually, two categories of users might be unhappy---or, rather, intrigued---after the fix.
a) those users who initially wanted their text left-aligned, saw it centered because of the bug, had resigned themselves to the buggy behaviour and now, after the fix, saw things displayed as they originally wished;
b) those users who did want their text centered, and at first clicked the Center toolbar button, then one day realized that this was not necessary since leaving the Align Left default button clicked gave the same result. It's impossible to know if those are in the majority. I am of opinion that it does not matter, as they can always edit their D. & D. and center their text if they wish to do so. And this minor inconvenience is balanced by the major advantage of making things work as they should.