Idea:

Generate multiple nonces, send to multiple addresses, include all the
nonces with the invoice of course.

This prevents guessing what a payment is for just by the price tag,
and differentiating payments from change.

Taking a step back, I am thinking about these proposed address
groupings as "single use accounts" rather than single use addresses.

An account being a group of addresses grouped for some purposes,
possibly for a single use payment.

In most cases an account will be a seed and a group of identifyers
(like nonces). I think this covers both bip32 accounts and stealth
addresses.