The problem is the same old: you lose a major glyph. You don't really want to lose DS because you're using it even more often with this rotation, and we know how good the other 2 glyphs are, so what you need to calculate is:
+ one DS instead of PS IT
- less RP
- one less major glyph
- one less HS
I really doubt the damage difference between PS IT and DS is higher than 1 HS, 5 RP and one of the 3 glyphs.
But its fun!
No, srsly i was just thinking about my 50/0/21 test DK with UB. Without DRW there is a free Glyphslot anyway.
But since DRW rules and will be way easyer to use in 3.2 you are right about that glyph
But is the math realy that simpel?
IT PS DS HS HS - DS HS HS HS HS
DS DS Pest HS - HS HS HS HS HS HS (in the final rotation)
so in in fact you do not lose one HS but gain one with both plagues up (which may proc sudden doom) (6 vs. 7)
what you do is exchange IT for Pest and PS for HS since you do 2 DS in both rotations (dunno where you see more DS?)
btw pest generates no RP? (dunno where u got that -5 RP from?)
So we finaly look at:
-one more HS
-2. HS target plagued (more dmg?)
-constant plage spreading (critting plagues in 3.2 anyone?)