Perhaps this type of service would even warrant its own dedicated
carriage to fit all the surfboards and baggage of passengers heading down to their second homes, like an active travel class 153 on steroids...
I don't think that's a smiley. In more sensible days, it'd probably have a full BG (brake guard) for luggage.
People moan about the seats on IETs, but actually the biggest flaw in the IET project was having commuter* interiors for long distance services. It simply doesn't work. Yes, Lumo sort of make it work for their services by restricting luggage to basically what a traditional airline offers to carry on, but they're an add on you can use to save money if their restrictions are acceptable to you, which kind of works because most of their traffic is going to be short city breaks, it's not the main service and it's not primarily people going for their annual bucket and spade which the Penzance very much is in summer. Bristol to London isn't much more than West Midlands Trains with a pointy nose, to be fair, and the IET as built is fine for those, but the GWR services that turn left at Reading (bar the Bedwyn) are very, very different things indeed.
It is very notable how doubling the size of most luggage racks on Pendolinos has largely fixed the luggage-in-doorways problem on those. The only place it hasn't is Coach A where the rack hasn't been expanded, funnily enough.
* Yes, with end doors, but things like luggage provision aren't really much better on the GWR units than a Desiro.