Why not just go ahead and ride the perm .... entering Wales is permissible from the 12th of April, and 600s hopefully return from May 17th ... what are you all waiting for ?
There are more 'views' to be had on the perm too ... and you all know what that equates to.
I believe (for what I've read elsewhere) that the A479 over Pengenffordd is still closed to cars (but sort of open to pedestrians?) - so still traffic-free. Google maps still routes you over it if you're driving, but Traffic Wales has it closed until October.
Here's the Permanent route:
https://ridewithgps.com/routes/32249809?beta=false Obviously other route variations are available (eg Hay to Monmouth) but this is my best effort, and the route I'd take. As a Permanent (BR) with you'd get 42+ hours for the distance.
"Chepstow depart/arrivee: Usk, Rhayader, Borth, Barmouth, Caernarfon, Menai Bridge, Llanberis, Betws-y-coed, Dolgellau, Newtown, Llandrindod Wells, Hay-on-Wye, Monmouth. The route can be ridden either direction."
Going via Llangorse is 3km longer than the 'closed' A479 (landslip).
Edit: This is a route based on @Blacksheep's perm.