If your ping above 1000+ you shouldn't even play this game. Everything should be unable to be ping kicked except fighting, that's what the people want? bad idea. And wait, before jailed you did some action like killing cops or play an event? this asking for a good ping too. You did well by making this suggestion but unfortunately I'll down vote.
Not too long ago it was suggested that if you are in AFK mode you cannot be ping kicked. I'd like so suggest a similar idea but this time if in jail, sometimes you get a long jail sentence and you might leave the PC only to come back to see you have been ping kicked. You log in and see you only did 100/2k seconds, and all that time was wasted. Seeing how you cant jump/do animations in jail, I don't think this would be abuse-able.
I agree with you, what about just allowing us to do /afk in jail ?