The device limit is based on the capability of your router in one location. If your router is stronger and expanded, it can support more than 10 WiiM minis. But the wireless interference maybe serious sometimes.
We will release a next generation WiiM Product named WiiM Pro. WiiM Pro has support ethernet port that will avoid the interference between WiiM Products, we plan to release it Q4 this year. So we suggest you to use WiiM Pro to establish whole home playback.