I'm going to have to go against my fellow mods on this one.
I think readily available EBRs other than the AR, at similar prices would sell like hotcakes.
A lot of things have changed since the gravy days 86-89. I'm willing to bet that the market for black rifles has grown greatly since that time. At that time you could get an AR or any of a multitude of rifles for similar prices.
Now however times have changed. Since '89 the market has seen a few things happen. The consumers have been pretty much stuck with one kind of weapon, the AR was really your only serious .223 black rifle option. Also during that time the market was conditioned to believe that the foreign guns were somehow better. Caused of course by high prices (in reality a function of supply and demand rather than quality) and the old grass is greener on the other side of the fence syndrome.
How often do we hear people who have never actually even seen one go on about the superiority of some other weapon system? But they have built that system up in their mind to be better. It is all perception. And in marketing perception is king.
Another factor that would help out another .223 EBR on the market is the fact that there are many of us, who have used ARs for years who are not entirely satisfied with the gun. Now don't take this to be a bash on the AR and don't feel the need to jump in and defend your baby or call me a couch commando or any BS like that. The fact remains that for us PERSONALLY we don't like the AR for whatever reason. Booya, instant new EBR market.
Of course HK failed with the SL8. The damn thing costed a fortune, and it only took neutered magazines. Where is the selling point other than to hard core HK fanatics. If they made a domestic version that took commonly available mags, (or regular mags when the AWB dies) and it sold for AR prices then it would sell really well.
The M96 does okay, but its price is close to double that of an AR. If there was an $800 M96 it would sell much better. No doubt in my mind.
Look at the AR180b. Brand new gun. Hard to find because they get snatched up as fast as Armalite can get them out the door. Only one manufacturer, no real after market stuff, not fancy at all, and right now they are going for scalpers prices so that they aren't that much cheaper than an AR.
Us gun folks like diversity in our safes. Give us more options at a competitive price and they will sell very well.