Firesight Management Center is required for all FirePOWER instances - hardware appliance-, virtual appliance- or ASA module-based.
That's the way it (prior Sourcefire Defense Center) was designed and built by Sourcefire prior to the acquisition by Cisco and that's how it is today. I doubt we will see that aspect change as it's pretty fundamental to the product architecture.
One small change is that if you only have the ASA module-based FirePOWER services there are special SKUs for a low cost FMC for managing either 2 or 5 modules. So, as that demonstrates, licensing is up to Cisco to determine.
Feel free to convey your thoughts on the matter to your Cisco or partner account manager. I have! :)
