One measure that would be pragmatically helpful, would be that if the down VIC to SOU train is so late (usually 20 mins or so) and is stopped (PINEd) at Fareham, the staff at Fareham immediately telephone the Southampton staff and advise pax off the Weymouth line (arrives xx.58) to stay on the platform and get the GWR service to Portsmouth (at approx xx.06), instead of crossing over the bridge to get the xx.13 to VIC that's never going to turn up. This depends, of course on the GWR being reasonably on time, but can mean that, equally usefully, one simply gets off at Fareham and waits for the PINEd train to roll in from the siding behind it.
There are other measures that could be useful, if the down service is PINEd at Chichester or Barnham or Horsham (all happen frequently) but on my recent trip from Dorchester to Gatwick, the public address at Southampton just droned out an automated message recommended changing to SN, although I already knew from RTT that the SN was completely up the spout - I mean no trains at all for hours along the coast, not even late ones. Had I not decided to go via Clapham Junction and Croydon, we would have missed our flight. I imagine that it's highly likely that several people did.