I thought of units and buildings having their build/train icons. Here are my ideas:
Building: (tech faction)
Press 'B' to open build menu
Press 'Q' to build the first building (farm), 'W' second building (barracks), 'E' third building (blacksmith), 'R' fourth building (castle)
Press 'V' to open advanced build menu
Press 'Q' to build first building (technodrome), 'W' second building (tower)
Training: (barracks example)
press 'Q' to train first unit (swordsman), 'W' second (archer), 'E' third (guard), 'R' fourth (horseman)
Summoning: (summoner)
press 'Q' to summon first unit (daemon), 'W' second unit (ghost armor), 'E' third unit (dragon)
This hotkeys can be of course changed, retaining it for first, second, ... units will be consistent with all factions and mods, generally first letter hotkeys are already passe. Also to be able to change it may fix some issues with different keyboard (like AZERTY instead of QWERTZ and so on). The problem may arise if too many units/buildings are available at single factory.