All 2004 MY turbo Subarus (WRX, STI, F-XT, Baja Turbo) are already CAN compliant. The transfer speeds out of the new ECUs are incredible, I get updates on my DeltaDash/ECUtek console as fast as 20ms. I'm currently connecting via RS-232 serial at 230Kb/s. The live graph plotting is wild, it's as close to "realtime" as Subaru telemetry gets right now. As the speed of serial devices improves, it will only get better... the ECUs support something in the range of 1.5Mb/s transfer, which is huge for sensor data. In comparison, the previous OBDII ECUs topped out at like 19200 baud.

The '94 and '95 SVX ECUs have all the information available through a scantool that OBDII has (plus a bunch more) but are not technically OBDII compliant due to differences in their connection plug.

With the proper OBD->SVX adapter you can pull some of the codes on an '94/'95 with an OBDII scanner, but it depends on the scanner and the range of protocols it supports. The Subaru Select Monitor (tool that all Subaru dealerships use) interfaces with all years of SVX in "native" mode and an incredible array of live sensor data is available.