Why not make the replay button go to a public reply automatically and make people use the drop down for private or whatever. I'm sure people will figure that out.
The post navigation bar has had more debate and revision that anything else, by a mile. There's a large number of possible links and a large number of scenarios, ads, no ads, stock or non-stock board, replies or no replies, next, prev, next batch, keep, last read, report, etc. Desktop, large mobile, small mobile, portrait, landscape.
We'll make some more tweaks.