I don't see a particular reason for this, TBH. The sweet spots will be likely dependent hardware / OS configuration etc. Assuming there actually are sweet spots - no one demonstrated that yet.
Also, I don't see how supporting additional WAL sizes increases chance of incompatibility. We already allow that, so either the tools (e.g. backup solutions) assume WAL segments are always 16MB (in which case are essentially broken) or support valid file sizes (in which case they should have no issues with the new ones).
If we're going to do this, I'm in favor of deciding some reasonable upper limit (say, 1GB or 2GB sounds good), and allowing all 2^n values up to that limit.
I think the majority consensus is to use all valid values. Since 1GB is what we have finalized as the upper limit, lets continue with that for now.
