"At the one-time expense of having to learn to recognize letters and words both ways"
That is a very expensive expense, though. And the result might still be worse.
I can quickread a page in a couple of seconds, because my brain memorized the shape of the words and even sentences. It took me years of lots of reading to achieve that.
I am not sure if my brain could handle the double amount of shapes, because this is in effect what would be needed.
And eye movement is very quick. But feel free to give the experiment a shot and share results.
(it should be trivial to write a script that rearranges text that way)
> That is a very expensive expense, though. And the result might still be worse.
That's entirely possible but it is hard to tell without going through the entire learning process. There might be a lot of redundancy (as we can quickly recognize mirror shapes) which if tapped at an early age might make it actually a trivial "add-on".
Anecdotally you can learn within minutes to slowly parse script in reverse order. Whether you can ever get to the same speed is not clear. We do know that some cultures did use alternating script (so its clearly not impossible) but we also know that they abandoned it in the end - so there might be some disadvantages.
Maybe the reason for eventually adopting uniform LR or RL instead or alternating is not the difficulty of mastering mirror versions, but being able to quickly start reading from any line on a page. For example finding the spot where you left reading, or scanning to find a relevant part. For this task the alternating form is actually less efficient as you need to jump back and forth as you go down (or up :-) the page.
It shouldn't be too hard to make a chrome pluggin to render comment threads like this in alternative forward and mirror / backward lines. As you say reading mirror writing isn't too hard so you could sort of slowly get good at it while wasting time on HN anyway. Would be a fun silly project might give it a go.
That is a very expensive expense, though. And the result might still be worse.
I can quickread a page in a couple of seconds, because my brain memorized the shape of the words and even sentences. It took me years of lots of reading to achieve that. I am not sure if my brain could handle the double amount of shapes, because this is in effect what would be needed. And eye movement is very quick. But feel free to give the experiment a shot and share results.
(it should be trivial to write a script that rearranges text that way)