If you want your rear cover and front upper handguard to cowitness, you can't use a low rail that would cowitness w/ irons that would also be on same level as railed receiver top cover...
Personally, what I would most like to see is just a railed receiver cover, in two versions.
The first roughly same dimensions as stock receiver cover, just w/ a rail. And the second a longer that engages w/ (EDIT:) rear edge of rear sight block and also incorporates some sort of brass deflector to allow a scope to extend across the full length...
So for those two, you have no domestic competition and are not competing w/ investments folks already made in forends...
For instance, the Mako polymer forends are only $60 and are at a price level where you really can't compete. But if you made your rear rail covers at a height that lines up with those and then also made a separate two piece forend out of aluminum that did the same (one company out of Ohio makes an upper, but not an upper and a lower -- I like and need a railed lower more than upper...), you'd have much higher profitability IMO...
Conceptually, I get the utility of a one piece rail, but if I'm losing my iron sights and completely changing the aesthetics of the rifle, a lot of folks/enthusiasts won't be interested.