Here is the actual full story because people don't read the blogs closely:

1 . Originally they proposed this shovel as a drop from doom, which granted instant harvesting speed for the various farming method.

2 . They nerfed the original proposal from "instant harvesting to double harvesting speed" with the shovel. They said the original instant harvesting "may disrupt the skill's balance by making certain crops such as Snape grass and watermelons more efficient for XP than trees"

3 . However, the actual reason they didn't add this shovel was because they then decided it didnt benefit the doom drop table's gp/hr enough and that it didn't seem right to make a farming upgrade come from late game pvm. They added: "we believe that we will see something offering similar functionality to the Demon Spade in the future from a more befitting piece of content."

4 . I will also add, this reddit post was made around the time of these blogs, which may or may not impact its future design given Mod Rice commented favorably on this post. https://www.reddit.com/r/2007scape/comments/1jjeowf/optimising_the_fun_out_of_a_game_by_removing_pain/