DiamondDude11

You could try doing speedruns in the category yourself, to make people know that you really want this.

Thanks for that idea! I might do that...
Do they allow GZDoom for submissions, or do I have to play on a completely new sourceport?

GZDoom demos/submissions will become incompatible with the most recent version the moment a new one releases.

Demo-compatible ports like PRBoom+ are used to mimic vanilla doom, boom, etc. This way, demos you make(if following said compatibility levels) will stay compatible forever, and can be viewed however many years for now!

Thus, the speedrunning community tends to prefer demos made using PRBoom+ or the source ports/versions of doom it emulates.

So yeah, you'll have to learn a new sourceport.