I think the more important issue is if there is a market for a new rifle in .223. Everyone and their brother is making AR's these days. The .223 market is full of high quality rifles for $1500 or less. When you look at other attempts to build a non-AR .223 they have all been a relative failure. I've never seen a kel-tec in person in a gun store, be it the little mom and pop store or some of the biggest in the state. The ACR and SCAR have sold in limited quantities at best. The XCR has been around for a while and is at best a niche rifle. The mini-14 has had good success but if brought up today as an item for purchase, at least most forum posters trash it's performance compared to the AR. There are AKs in .223, but again, far from an overly common item. There are the MSAR and AUG type rifles which made an attempt but didn't do much. The FN options were video game cool but have been a novelty at best.
My point is that, at least in the US, you don't see any other current production .223 really holding a firm market share. While certainly there were other 9mm pistols out when Glock came out with the 17, it had a new twist using polymer when everyone else was using steel or aluminium. They had a unique and quality product that did things better than a lot of other current designs. Not to say that the 17 was the perfection Glock makes it out to be, but it had some advantages over the then current market. Polymer rifles have been made in .223. Metal rifles have been made. Piston rifles have been made. High quality, highly reliable, highly accurate, mildly priced rifles have been made. Unless a new company can capitalize on such a shift as when Glock introduced a quality composite pistol in an all metal world, I don't see another .223 rifle doing much to slow the sales of the AR based rifle. Maybe if the SCAR, ACR, or XCR were priced at $850 we would see them compete, but it doesn't seem like that will happen so I don't personally expect to see the AR system lose much market share to another design.