OPI is more or less defunct nowadays.
Computers are far more powerful and networks are far faster than they used to be, effectively eliminating the need for OPI systems. Throw transparency effects into the mix and OPI even becomes a hazard (InDesign needs the high-res images to flatten transparency for printing)!
I'm sure that some OPI systems still exist and quite possibly some of them work with transparency, but the cost of installation and administration of such a system outweighs any benefits for most uses these days.