I guess this has now been implemented in Sequoia, using the EBU standard. Will this be possible in Wavelab 8, and if so, will the ISRCs be derived from the individual codes in the montage?

ISRC is not part of BWF. However, WaveLab lets you transfer montage’s ISRC in any part of the meta-data (custom field of BWF, ID3 v2, etc.), thanks to the concept of “variables” (some special variables are pre-loaded with certain information, and can be inserted in any meta-data field). You don’t need to type your ISRCs again.

The EBU came up with a standard last year. They put it in the aXML chunk. Sequoia just recently adopted it.
(the document, not the article, is from last year).

btw that’s good news about the variables. Didn’t know about that.

WaveLab 8 supports aXML chunks, hence it’s possible to automatically insert IRSC codes inside it. What you have to provide (once, and store it as a preset), is the other “surrounding” stuff you want to have in the aXML chunk.