I have enough knowledge to answer some questions you asked.
jschan is "production ready" in my opinion, tom has said that the notice is just a disclaimer that he considers jschan hobby software, and he probably doesn't want people angry if something breaks. Newer sites seem to want to use jschan, or at least try it. I've used the mod tools on vichan, lynxchan, and jschan, and lynxchan is by far the worst (no contest). jschan's are quite good thus far. jschan can take some getting used to for anons due to post formatting differences, for example spoilering text is handled differently. jschan development is active (like lynxchan) and tom is more open to implementing good suggestions than stephen lynx is. As far as I know there are no scripts to migrate from vichan or lynxchan, but anyone familiar with the db structure would probably be able to get it done.