I get all your points and I think they are the reason this has not been solved yet. But at times like this, i take inspiration from the story of first version of Captcha that, I think, Yahoo! created. The simplicity of using two words, one known and the other unknown to practically get all-printed-words-ever transcribed is nothing short of awe inspiring. If the Indian government were to put all words in regional languages as a part of Indian version of such Captcha just to book tickets on Indian railways then the entirety of regional language text could be transcribed before we know it, besides giving valuable training datasets for ML/DL models too.

Nonetheless, i wish you the very best in your endeavours.