This topic generally came up during the previous AMAs. We were previously told at various points that the team was exploring additional rewards/incentives for players to review.
Currently, upgrades are the only reward we get for reviewing. Given in recent years, nominations got decisions at a much faster pace. We had eMiLy auto-accepting nominations within 24 hours of submission for nearly 7 or 8 months, so there was no point in upgrading nominations.
Upgrades used to be a great motivator to review, but I personally would argue that they are not enough of a reward for reviewing.