The only thing I would wish to see implemented is a fee forecast so I could time my payouts a little bit.
Adjusting the fee so that it can be set to high/low priority?
Mostly, exchanges and casinos usually use suggested good fees enough to get acceptable waiting time for confirmations, so I don't think that payouts from casinos or exchanges require too long time to be confirmed. Usually, it takes around 30 minutes to 3 hours, in my experience. For windice.io's payouts, I have no issues with payouts from the site, because it fastly passed by the site, and then often confirmed within 'normal' waiting time. Personally, I don't think the site should implemend the manual fees setting for users. Because users might choose too low fees, that might cause their payouts stucked. Then, complaints, support tickets will increase. The site can set a fixed minimum fees, and allow users to set higher fees than minimum one to boost their payouts faster.
the users cannot choose the fee manually , not a single casino has this option (maybe c-games has the closest to this where you can drag the slider withing certain limits and pick the fee)
some of them give you 2-3 options as in 20-40-60k satoshi , for example
but the vast majority have a set fee , it is easier this way and the system , usually , picks the fastest option
there could be times where the mrket situation changes and the mempool gets overloaded and your normal 10k satoshi fee is no longer cutting it , it happens too but not very often
windice has set the upper limit for the feee , it is 20k satoshi now , if I'm not mistaken
the times I withdrew it was way less then that , think I paid under 10k