Talking with friends and neighbors, it seems a huge barrier is the technical nature of Bitcoin e.g. understanding it in general & how only computer-savvy users can set up a mining rig. But better and better videos are coming out explaining Bitcoin - and I guess they could always buy a pre-built mining rig 
I'd be happy to set one up for them too 
I'd be happy to set one up for them too Gold wouldn't have worked well if almost everybody interested in using gold was able to mine it though!
I think mining should be a small part of bitcoin, at least much smaller than it is at the moment.