I think it would be workable in a VTT but a complete pain in a pure MMO.A VTT could certainly have helped with tracking situational modifiers. However, 4e was fairly streamlined in that respect when compared with 3.x and its nearly endless potential layers of buffs. If they'd wanted real value added, they could have kept things like Bull's Strength adding a Strength bonus for several hours. It's a PITA to track at the table (IMO) but fairly simple for a program. Just add a clock the GM can advance and even the buff expiration can be automated (to say nothing of interactions like Dispel Magic).
IMO, the situational modifiers and reaction triggers would have been a pain to develop and maintain. Certainly feasible, but having so many different situational triggers would have required each one to be coded for. Things like tags could have helped, but having so many conditionals would have created an environment prone to software bugs.
That suggests to me that 4e was designed with the TT experience as the priority (as opposed to the VTT).
Edit:
Of course I have not tried to program a VTT.