- Should we integrate smart expression templates? I think there was a gsoc project but I am not sure. What was the output?

​it was really good
- Are (smart) expression templates really required?

​but after second thought, I wonder like you.
- How often do expressions like A = B*C + D*D - ... occur in numerical applications?
- Should we provide a fast gemm implementation of the Goto-Algorithm like in Eigen?

​why not.
And regarding the code infrastructure:

- Do we need iterators within matrix and vector template classes? Or can we generalize the concepts?

​once there's been a discussion about that. Can we factorize all this code into one place, one generic concept ?
This would make things so simple and efficient in the end.
- Can we maybe simplify/replace the projection function with overloaded brackets?

​Can we do that ? That would be awesome !​
General questions:
- Shall we build uBLAS a high-performance library?

​Yes, I suppose.
What do you mean exactly by "high-performance" ?​

- Could it also be a convenient wrapper library with good interfaces to high-performance libraries such as OpenBLAS?

​There's been a lot of them written over the years. They're old now and having a simple way for the user to choose a "backend" would be great.