1. It's not a 100 motes, "only" 20 :-)
2. I said, "even with infinite penalies"; as is, you can have 16 attacks, 8 of them at your max attack bonus -4. Taking a Red Dragon as an example again, they'll hit on a 2 with sufficiently optimized build :-)
Edit: I guess I have to clarify my math a bit.
You have 4 attacks as a Chm20, plus 2 for surge of battles
Then, you have 20 motes invested into Twinned device, giving you 4 additional weapons to two you get from TD, for a total of six; with Greater Multi-Weapon Fighting you have two attacks from each of them, for a total of 10.
Of these 16 attacks, you have first attack from each weapon, and 2 from Surge, total of 8, at your max bonus (-4 for multi-wield). Rest are iterative attacks, 6 at -5, one at -10, and last at -15.
Of course, you can only use Surge when you need a bit of extra edge, using "only" 14 attacks, 6 of them primary, on other rounds, and having 20 motes open for Blasts or Barriers or whatever...