That PDU doesn't take up very much space. If density required it, 4, 6 or even 8 is completely feasible, however if you're running a 40KW rack, you'll probably want to think about 3-phase.
Instead off say a 60a 208v 3ph PDU, couldn't someone just get 2 30a 220/240v PDU's, space permitting of course ?
Might just mean an extra outlet / breaker etc.