I'd say temperature regulation is a problem that hits before street condition and darkness. Even before it's too dark and too slippery for most people to ride, there is the issue of keeping one's body temperature adequate: not too hot, not too high.

In my personal experience, this has required a lot of experimentation, and I'm still experimenting. But I take it for granted that I'll have a shower at destination, so I don't mind if I get too hot. If I was cycling in the plain clothes that I wear through my work day, I'd be a lot more reluctant to keep doing it when the conditions change.

Here there is also the added problem of rain.

But, if a lot of your co-workers have only a short distance to commute (less than 5 km) I'm sure you can convince them to try it.