If you're only getting 59Mbps then g.fast will almost certainly not work, the only two exceptions would be if cross talk is severely affecting your line, or your line is banded, although that would suggest your line has or had a problem.
G.Fast uses higher frequencies than vdsl, and if you was using the full range for vdsl you would have much nearer 80Mbps.
The cabinet addition could just be for more tie pairs, usually that sort of extension wouldn't have vents, but this has been reported recently, perhaps they are just using up old stock.