Barmaley; They were nowhere years ago and burst onto the scene as the cheapo (cheapest) PLC you could get. They were EXTREMELY low cost. Under a hundred bucks if my memory serves me. They actually sold them door to door. I remember a kid showing up at my company pedalling them. I thought he was another door to door suitcase salesman and was about to kick him out when he whipped out a PLC the size of paperback book. It came in modules, buy what you need.
That was the beginning of the major price drop in the industry. I had just used a $57,000 Allen Bradley and was amazed.
So anyway this was about 15 years ago and they are now pretty common so to answer your question; I think they will be around for quite a while.
I looked into the Keyence PLC's a couple of years ago, they were going to give me one to try. But, after downloading and using the software I decided against them. They may be great PLC's but the programming software is about the worst I've ever tried. The salesman was upfront about the software being a little below standard, but when I actually tried it, I found it was way way below standard.
But, the software was free and I guess you might say worth every penny you pay for it. :=)
