if religious texts can't be converted into more modern media types will they become irrelevant or indigestible?
Religious texts ARE converted into more modern media types. You can access the texts of all the major religions online nowadays. And even if some more obscure religions refuse to convert their texts, their adherants will simply continue accessing them the old fashioned way.
isn't it weird that some media - eg the bible - coming in incomprehensible book form, has lasted so long? people probably know more about game of thrones than the bible overall these days though. of course there is Christian music, for what it's worth.
Tao te ching is short and well translated and yet there are not many taoists.
The Bible is far from "incomprehensible" -- I read through and studied the entire King James version in my teens. Sure, it's a tedious read and most of it is frankly irrelevant today, but that doesn't stop the believers from insisting that it's "God's Word." Because that's what they were brainwashed to believe.
It's lasted so long thanks to indoctrination
. Religion is all about location, circumstance and numbers; even if the Tao Te Ching is brilliantly translated and more relevant than the Bible, there simply aren't many Taoists in Western societies -- so not many children get indoctrinated into it. Christianity is currently the world's largest religion thanks to a long, bloody history that most modern Christians are content to ignore; just as the growth of Islam can be attributed to their violent expansion over the past millennium. It's still a crime to be an atheist in many countries around the world. Plus most people are unable or unwilling to overcome the brainwashing that they were subjected to since very early childhood; we're evolutionarily wired to trust our caregivers, so it's only natural for children to internalize everything they are taught.
And until very recently people didn't have access to outside views; most people grew up in small, insular communities where access to information was extremely limited. Even the Bible was only printed in Latin up until the 1500's -- heavily restricting the common peoples' access to it. I think it's very interesting to look at the statistical rise of religious "nones" over the past few decades -- since the invention and popularization of the Internet.