Thank you for raising this question, I think it's very a valid one. I am looking at the ways of removing mucoid plaque myself, but would be more reassured if there were some scientific facts about this and I knew how many people actually have this.
I was asking a friend who works as an operating theatre assistant just a few days ago if she came across the plaque and her reply was that the colon just looks pink - I was rather hoping she'd say yes, she sees the plaque all the time.
In the meantime, I guess we have to go by the empirical evidence on forums like this and assume that many of us do have it.