Shapley value (https://en.wikipedia.org/wiki/Shapley_value) – a game theory solution proposed in 1953 in by American mathematician Lloyd Shapely to determine how rewards are proportioned among individual members of a team. The Shapley value attaches a real-value number to each player in the game to indicate the relative importance of their contributions.
As of now, the delegates are considered to be equal in terms of how much they contributors to the system so the rewards are equal (according to symmetry property of Shapley value). That also means if we introduce other types of delegates (e.g., IoT devices that play a weaker role of delegates – they only validate/endorse txs rather than producing blocks), their rewards should be calculated using Shapley value.
This principle also applies to campaigns like delegates-of-the-month, assuming it is feasible to quantify the contribution, e.g., by voting or by the number of txs a contribution produces.