Yes, but, the problem isn't typically being proprietary, when it comes to future use, but a closed, non standard, unknown format.

Yet you're creating a new standard here, with your own rules, which no one will understand, and which no automated tools can convert to another format.

(Eg some kind of table formatting)

Better to be 100% html than this.

(Maybe you meant that, but regardless, this is a good place for me to comment on standards being more important than anything else.)