When I started my rust journey Diesel and Rocket were the first few crates I worked with and it really opened up my mind and I haven't turned back since.
As for async, my primary concern for that was to make sure you minimise blocking code calls in your futures. Even if there weren't many performance gains to be made from Diesel itself being async but having database calls marked as Futures could theoretically help the runtime schedule and manage other threads.
I'd like to thank you for you amazing work once more!