I've been using trains with bikes for the past 15-20 years. I noticed a lot of people having trouble using full size bikes with trains but this is where folding or collapsible bikes come to play because once covered, most rail lines won't have any issue. I've taken my Brompton on Amtrak and never had an issue. A full size bike would have created problems.

I've seen on YouTube a number of people using soft bags to cover a full size bike. However, the issue of removing the derailleur is a pain so I recommend using a bike with an internal gear hub if you're going to collapse it into a bag.