We love camping with our Ollie. Always wanted to improve Ollie's windows, too.
On our previous camper we had Euro Style windows that could be opened up to about 70 or 80 degrees and had nice looking shade/screen assemblies. We really liked those windows because we could leave them open during a rain that is straight down. On the down side they were single pane plexiglass. Another issue that could happen with the Oliver is deflecting water above the window when open due to the hull angle, I don't know but have wondered about this issue if using different windows.
With so many good ideas posted here, I'm sure from time to time Oliver looks at certain modifications/improvements. Before retirement one of my jobs was to answer warranty claims for industrial machine components we rebuilt or had built by other manufacturers for a fleet of 2200 machines. Sometimes it's difficult to see criticism of work your teams produced, but to be honest it was very helpful for us to improve and produce the best product we could.
Here's a Euro style window similar to the window we had in a previous camper:
https://aussietraveller.com.au/products/eurovision-window