What makes you think it will just be a cameo? Nothing I saw in the article gave me that impression, and I would think if they're going to go to the trouble of making a big announcement like this, it's going to be more than just cameos.
I don't know. It felt like the LoT part just seemed bigger (being an "unannounced character"), and I do kind of wonder what Diggle would be doing to just randomly show up in everyones shows for more then a cameo.
To be clear, I'd like to see him have a full guest role, it just feels more like a cameo thing to me, at least for some of the shows. I could be completely off target, which is fine, it just felt more like a cameo thing to me, at least for some of the shows
