There are some mods that players can currently only get one of unless they buy them from another player. Mods such as the Umbral and Sacrifice mods aswell as the Amalgam mods from Thermia Fractures.
A while back they introduced the ability to buy quest warframe parts from Simaris, this allowed getting multiple of quest frames which was impossible before.
Would it make sense to allow multiple of these currently one time mods?
One example of where I'd find such an addition useful ca