^^^ In basic terms, an entire aftermarket case would be prohibitively expensive. Very few people would be willing to spend $1,500 at minimum just for a 5mt case to house their expensive gears. Actually, with fairly low production numbers, it would probably be a lot more than $1,500. Making large cast parts with multiple locations that require precision machining can get very expensive in small scale production. For that kinda money, you could use a much stronger 6mt case and put expensive gears in that.
That's why I'm trying to keep it down around $100 for the main reinforcement and about $50 or so for the diff brace. Folks are more willing to add a little stregnth at an affordable price.
Funny side note that I found during testing: The upgraded hardware accounts for about half of the reinforcement's stregnth. Dimensional change was measureably decreased with the stiffer/stronger bolts holding the reinforcement in as compared to some class 8.8 bolts I tested (equivalent to stock, but longer to accomodate the reinforcement). Needless to say, I'm looking into putting a full class 10.9 5mt bolt set together in the near future
I haven't finished the write-up on testing with the reinforcement on, but with the reinforcement and improved bolts installed, it took about 350ft./lbs. of input torque for torsional distortion to equal what you'd find in the case at the stock 230ft./lbs. without the reinforcement. So basically, it still flexes with the reinforcement on, but it takes quite a bit more torque to get it to flex the same amount... Which is pretty much exactly what I was aiming for. And the diff brace cut flex roughly in half at the peak point of expansion just above the driver's side axle stub... I measured a bit over .003" at stock torque without the brace, and that figure came down to just a barely crossing the .001" mark on the dial gauge with the brace installed.