I'm pretty OK with expecting client drivers not to be stupid and offer escape syntax for their placeholders. I was kind of astonished the jdbc spec doesn't given how hard it works to be compatible. I'd assumed the ?? was jdbc standard not a postgres extension until I looked into it.
Certainly PDO needs a patch for its postgres driver if not (preferably) to support escaping at a higher level.
Users can work around it by defining their own operator aliases + opclasses or using function forms.
Doesn't seem worth too much drama though it sucks for usability.