To provide a bit of metagame context to this, I think Doom Desire is much more, well, desirable than Future Sight. The plethora of powerful Psychic-types will make it tough to balance a Future Sight CAP26. On one hand, it has to compete for a teamslot with Tapu Lele (a slower wallbreaker), Mega Alakazam (a fast but frail sweeper), Aurumoth (a powerful setup Pokemon), Mega Medicham (blows up Chansey and most Steel-types), and Mega Latios, which is a great tank. For a Future Sight Pokemon to compete in this kind of environment, it's going to have to be really strong or at least differentiate it somehow. And, if it does that, we risk it pairing with any one of the aforementioned Psychic-types. This would lead to a very unbalanced metagame. Now, process doesn't necessarily care about the metagame, but I think process will flow much better if we're not worried about carefully balancing options to make a Future Sight CAP26 have a niche, while also not overpowering in Psychic-Spam cores.

Futhermore, Doom Desire is just much more interesting in general than Future Sight. While it is an exclusive move, Jirachi hasn't and never will actualize it. Basically, there are 0 users of this move. As a project that explores competitive Pokemon, not picking Doom Desire would be a complete missed opportunity! Special attacking Steel-types that actually use their Steel-type STAB are few and far between. Yes, we have Magnezone, Magearna, and Naviathan. But, face it, Magnezone would be nowhere near OU without Magnet Pull, Magearna rarely uses Flash Cannon (its Assault Vest set runs Iron Head), and Calm Mind Naviathan doesn't run Flash Cannon. With Doom Desire, we'll make a unique Pokemon, even just factoring the huge increase in base power from Flash Cannon to Doom Desire. With a Future Sight CAP26, as many have pointed out, it'll be incredibly difficult to incentivize using Future Sight when its Base Power increase from Psychic is a mere 30 points. Doom Desire jumps up 60 points, which is much, much more effective. With these thoughts in mind, I think we can have a more interesting process that's not as worried about metagame balance with a Doom Desire CAP than with a Future Sight CAP.