Reopening Caernarfon - Bangor would make a lot of sense. It would then be possible to pick up the Welsh Highland to Porthmadoc to connect with the Cambrian Coast Line.

Once they sort ERTMS on the Cambrian Coast there could be quite a bit of spare capacity to run a container service up the coast, as long as Barmouth Bridge will take the strain, to supply Supermarkets in the area. Would be a lot cheaper and more environmentally friendly than trying to improve the roads. I have driven minibuses extensively in the area and know how slow it can be!

This makes sense on two fronts, both for commercial and for tourist traffic.
I'm over in Bangor tonight for the weekend visiting my youngest daughter.
I'll get her to do some enquiring to see if there are any plans for further developing the Caernarfon Bangor branch reopening.

What narrow gauge & standard gauge how woul that work?
There are few supermarkets in that area anyway
Tywyn has a Spar & a Co-Op which can be supplied with one ore two lorries each a week.
The nearest Sainsbury's supermarket in the area is in Welshpool

Commercially it could be an asset for shifting the masses of eBay and mail order packages that seem to be an endlessly growing market.
How often do the carriers send huge white vans for miles up country lanes to drop one meagre parcel.
Welsh Highland could create collection points at each station.
If worked in conjunction with the post office the Highland could commission parcels vans for attaching to their trains.
There's also potential to increase the tourist traffic by making access via rail easier.
My eldest daughter did her masters in Transport and Sustainability and works for The First Transpenine Rail. She is always looking for opportunities to utilise any form of rail traffic movements.