This is just a guess...but, I am thinking they would have to design a whole new action, rather than just modifying one that is already used for rifle cartriges. You know, a dollars and sense thing. There just isn't enough demand for that firearm and redesigning the action would most definitely increase the price which would only decrease the sales figures.
If I can get an idea of how accurate this lever gun is, that might give me an idea on what to expect if I shorten a H&R 26" 410 to 24" or 22" and make it a cyl. bore slug gun. The advantage then would be I could use 3" Brenneke's and may be able to get a 2-3 inch grouping at more than 50 yards. That would make it a nice brush gun.
So, if anyone has some personal experience with the lever 410 and would like to share, it would be appreciated. Thanks