Forget the norm. Do what best suits you.

If your site is not already run on a database, creating one *just* for the consent form can be expensive. In that case I would stick with the text file.

However, if the site is already run on a database, maintaining this feature through the database will not take much effort at all, and I most likely would suggest you do that.

There would also be other factors for you. My advice would be to weigh in the rpos and the cons to each, crossing out or amplifying each ones that apply to you according to you situation. In the end, you should pick hat is the best fit for your website, and not something else for the sake of conforming to the norm.