For: Donna is Harvey's closest confidante, calls him on his B.S. and even got fired to protect him. Oh, and they've already done it once! A flashback last season revealed that Harvey pursued Donna hard back in the day, but she rejected him because she has a rule against dating coworkers — until they were both simultaneously unemployed. Present-day Donna has also shown signs of possibly wanting something more.
Against: Is Harvey even ready for a serious relationship? He's attempting one with Scottie right now, but we'd much rather have him and Donna mainstain status quo until he's ready to commit. The last thing we need is an on-again, off-again relationship to ruin their impeccable chemistry.