Dave Hillam ]) gurgled happily, sounding much like
they were saying :

Why can't the ticket office staff being redeployed (presumably
outside peak hours) be equipped with portable machines like National
Rail travelling ticket inspectors who seem to be able to sell any
combination of tickets on their portable machines for any date up to
364 days in advance, and accept credit cards as well?

That's an excellent idea.

Well, apart from severely increasing the risk of robbery from what
would, in effect, be mobile unprotected cash machines,

It's hardly an idea without precedent - and I'd have thought that somebody
standing on a bus or in a ticket hall selling tickets was less likely to be
robbed than a machine standing alone at a bus stop... Besides, if National
Rail can do it, why can't TfL?

these staff wouldn't have an interface with Oyster.

Why not? Ticket inspectors already have hand-held Oyster wands.