I love branch delay slots, and they are a key feature for getting highest performance in the architecture I am working on... if you have things like guaranteed latency and static scheduling (like we do with the REX Neo architecture), delay slots are VERY useful in tight loops. I understand not including them in a general purpose design with branch prediction, but I'm not a fan of branch prediction and its effects on determinism.
I'd never heard of the Rex Neo until your post. Looks very interesting!