Michael R N Dolbear ) gurgled happily, sounding much like
they were saying :

For a single this is unlikely but since in your example even an
Z1-6 Travelcard is less than twice a £3.40 fare

Look past Zone 6.

For me, a pair of singles is over £3 cheaper than an ODTC - there
used to be an LT card in the middle, but that got pulled.

Not understood. I carried on with the OP's example. If you have a
further example let's see the details.

I'm in Zone B.

Single is £4.60
ODTC is £12.40
7DTC is £45.80

There used to be a thing called an "LT card" that was effectively an ODTC
except for not allowing use of (non-tube-fare) overland trains within the
zones. It was a tenner. It got pulled completely about a year ago.

When is 7DTC capping coming in on Oyster?

Probably never, the complexities, such as ODTC capping day by day, were
glanced at in a post on this NG.

Shame.

It would be the single biggest killer-app in terms of Oyster functionality
for me. I'm not in town every day - but some weeks I can be in four or five
times - but I don't usually know in advance how many.

Do I start the week with a 7DTC and risk over-paying because I'll only be
in three times?

Do I go for ODTCs and risk over-paying because I'll be in every weekday and
possibly at the weekend?

I doubt I'm unique, but it's magnified because of the ticket cost from
here.