So I did a fair bit of research about the mount coming with the deluxe edition and I can safely say that it will have scaling mount speed. Firstly the argument, it would break the 30+ twink bracket meta/PVP and make it pay to win to be able to run down people without that mount.
Now the proof, I compared other TBC mount “spells.” so in this case
You can see in the text that it says “this is a very fast mount” and though it has mod mounted speed 100% it is categorized different than the warpstalker
If you look at the section next to Used by item, “modifed by” you’ll see it is modified by Riding skill Journeyman which the Talbuk spell lacks. This is reflected in the text, and you can toggle Journeyman riding which changes the text from “Summons and dismisses a rideable Phase-Hunter.” to "
Summons and dismisses a rideable Phase-Hunter. This is a very fast mount."
This information is generally data-mined by Wowhead so it is safe to assume that the warpstalker mount has scaling speed and you will still need to pay for the individual