I Did It
I flew Jetstreams for ACA for 3 years before being hired by Gemini in 2000. Before flying the DC10 as a FO, the biggest thing I'd ever flown was a Jetstream 41, and I'd never flown a jet. Training was no problem - certainly no harder than any other training I'd previously done. I had a strong recommendation from a very influential pilot there which helped me get hired. There are a few others there with only commuter backgrounds, but they are few and far between - most new hires had extensive heavy or military time.
I left ACA for Gemini as they offered me an opportunity to fly DC10s all over the world - something I'd been dreaming about since I was a kid, and although I've since moved on to a more stable airline, the decision to go to Gemini was one of the best I have ever made. Schedules were tough at times - plan on doing 16 day trips, but then also plan on 15 days off at home in a row every month (you can easily work the first half of one month followed by the second half of the next and have a month off without losing any pay). Home basing means no commuting / jumpseating - you will be provided with a positive space ticket to and from home for every trip. If you like to travel, see the world and have long (3+ days) layovers in 5 star hotels in fascinating cities in Asia, South America, Africa and Europe, then go for it.