IIRC, Anki originally fully included any extra delay in answering in the next interval calculation. I think in 2.0 it was reduced to full/half/quarter, and more recently hard has stopped adding any delay at all. It’s mainly trying to prevent people from just completely resetting their cards, as seems to be a common desire when returning from a break: Due times after a break - Frequently Asked Questions
By how much, and how reliably could we predict it? I won’t argue it’s completely negligible, but would trying to account for the short term cramming give enough efficiency gains to be worth it, and not cause unwanted behaviour when cards are repeatedly reviewed? Users could send cards with short delays years into the future in the past just by repeatedly cramming them, and we definitely want to avoid that 
Yep, in full agreement that the transition should be smooth.