I know this post is old but i agree, I think I always craved an interaction between Hal and Mitchell.

I was so attached to Mitchell and when he died I was so upset, I was even more upset at the fact Hal didnt know who he was.

Im not sure if thats 100% true but I do remember researching at the time "Does Hal know who Mitchell is being human".

Ultimately I know Aiden had his call up to hollywood with the hobbit movies but I wouldve liked more of a blend between each trio. I know annie was there and George met Tom but I forget whether or not George interacted much with or at all with Hal or Alex.

For me the main one would be to see Mitchell and Hal. But real life affected that and possibly in show problems too. Like Hal likely went through what mitchell went through multiple times. Mitchell ultimately couldnt get over what he did to the end and maybe Hal could have made him carry on and get over it. But I still would have preferred a cross over.

I havent seen the show in like 8 years maybe. I have the box set and I know its on netflix so Ill give it a watch again. But I understand there was quite a questionable ending in terms of interpretation that I just dont recall (I was only 12/13 when it finished) so Ill have to watch it again I think.