The reason I bought FSD now is because the promise of hardware upgrades. Tesla is already developing a new computer. There's no guarantee that if you don't buy FSD now (it's already 5k vs 3k) it could increase even more later. There's also supposed to be the first features that require the FSD package coming out this year.
Tesla does have a completely different software in the works (Elon's talked about it, their AI head has talked about it, etc). The question is that software package ready in 1 year, 2 years, 4 years etc. Tesla will likely roll it out regardless of approval (since laws will be so gray around it, plus waymo will be rolling something out around the same time). Either way it makes more sense to roll $3k into the loan now than $5k later when I'm 3 years in and have to decide if I want a must have feature on my 80k car.
Ordering a P3D like I did also helps since the marginal cost increase is much less.