This is interesting. ATI is making a Polymer lower with a Zinc insert in the buffer tower for increased strength.

I've done a lot of testing with plastic and poly lowers and this is always where they break, so I am intrigued:

ATI Omni Hybrid Multi-Cal lower receiver

Link to article on Guns.com

At only $50 each, they are quite affordable. At the very least, this might make a nice lightweight dedicated .22lr receiver