I see that XMR withdrawals can choose between the standard and low-priority fees. Could you add a similar option for BTC withdrawals on agoradesk, either as a freeform “name your network fee” option or a “1 hour/24 hour/…” selector?
The main downside (beyond the cost of adding an extra field to the withdrawal page) is UX, since someone who sets a minimum fee could see their withdrawal stuck indefinitely. To counteract this, I’d propose putting big scary warnings or popups on the wallet page. Also if it’s not too hard to do, enable RBF and let users increase network fee on their stuck withdrawals from the wallet transactions list.
(I hope that feedback for agoradesk is also on topic here. Apologies if not!)