So, it would still be unfair for me to pursue a relationship that could potentially have negative consequences for both of them (from other coworker's opinions to drama between them) while I would be consequence-free.
Yup. I'd go with that one if it were me.
I enjoy crushes from a distance all the time. Just because you come across an interesting person doesn't mean it's the right one at the right time to try to take it to another level. We meet lots of people -- many right ones, not necessarily all the the right time.
I'll even go so far as to say there's people in our life who I know are open to poly, and I find attractive and could totally see trying to have a romantic relationship with because we're already friends.
But seriously? They've got full plates and some hints at baggage and I def have a full plate and some baggage with eldercare for aging parents and health issues... so this is just NOT the best time. I rather enjoy the crush on my own, enjoy the friendship, and leave it alone. Maybe that's all this is destined to be? I do not know yet. Time will tell.
I think your plan to wait and see and just sit with this some is sensible. Time will tell if Seamus changes his mind or you do or something else comes up.