What is ads.txt? Think about it as your whitelist: the companies you authorize to advertise your products or services.
Here is an example: https://elpais.com/ads.txt
In a data-driven world, with multi-touch attribution systems, it seems to me that a text file in your domain is not the more sophisticated way to public whom you trust your brand. Especially when this information can be used to authorize (or block) third-parties to advertise on your behalf.
I think it is a step forward in the right direction to fight ad fraud. As ads.txt evolves, I can see companies finding ways to automate how this file is created and updated and to use it for automatically whitelist publishers.
Or even alert the user if an ad fraud is in progress.