Interest payments down by over 50% in just the last 3 week 
That is correct. the average difficulty for September was 104,550,780 while this months average difficulty is going to be over 216,654,943 which is OVER a 100% increase.
Seems that money printing devices have seen somewhere around $100m in investment come in the form of 100% pre-orders and that investment has made the difficulty jump 30% more or less each diff period.
These are the risks along with manufacturer delay and BTC price.
And the BTC price has gone up with over 30% the last week, so It's not so big loss if we get 50% less BTC from Giga-/Teramining.
The BTC price will go up even more.
It's a big loss of bitcoins, for instance, I invested a lot of coins in gigamining shares & ended up with substantially less when I claimed for the 1530 shares that I had back in Feb, I got just 245 btc in back interest instead of the thousands that I'd invested, then I paid 382 btc for the paid upgrade to teramining on giga's assurance that this time it would be different, so far it's paid 173 btc less the 70.36 btc I would have received by sticking to the free upgrade, so 103 btc gained for a 382 btc cost & interest has slowed to 3.60 btc per week falling by 50% each 3 weeks on the latest figures, I don't see how this can ever cover the cost even with giga's assurance that he somehow intends to make it right.
The only honorable thing that I see now would be if he admitted the paid upgrade was a failure for those who took it & refund the cost of it, less interest paid out, but plus the free upgrade interest, which in my case would be 382 - 173 + 70 = 279 BTC or to explain when & how he intends to make this investment right for those who have supported him all along.
The 245 btc that I got back in Feb plus the free upgrade coins of 70 btc = 315 btc, these would be some of the very few coins that I had in my cold storage after the scams of last year, like bitcoinica, GLBSE etc, instead of that I am now 279 btc down atm just from taking the paid upgrade & earning a rapidly declining interest that can never hope to recoup this.
You're in luck! ~12 hours earlier from the time you posted the above, HashTrade made a $1M USD down payment to start up a premier data processing organization enabling all individuals to benefit from mining Bitcoins without having to purchase or operate any hardware.
Soon, possibly, you'll be able to upgrade. Rumor has it that all the Bitcoin mining rigs will be Monarchs, of which currently is all the rage.
~TMIBTCITW