Hi!
My first post here as I just went through this discussion.
I am no expert by any means and have just started hydroponics in the last few weeks.
I start many plants in the spring under
lights and wanted to eliminate all soil in my grow area. This prompted the same question you posed.
The best option I see at this point, and the option I will use shortly is rapid rooters in a starter tray on a heat mat.
For soil transplanting......Once germinated, up-potted into coir and placed in 4 inch pots until they can be planted in soil (containers and raised beds).
For hydro transplanting.....place the rapid rooter directly in the hydro medium and go from there. They seem to hold their form and resist crumbling.
Hope that helps just a bit.
Great forum and resource!