DKIM is already setup, the issue is SPF failing.
Adding an extra field to separate envelope-from and reply-to addresses will provide a lot of flexibility and enable SPF to pass as well (which it will not pass if one has SMTP server that forwards emails or doesn’t support VERP). The field can be hidden on the UI or even set to the match envelope-from and reply-to addresses unless the admins specifically decides to override. The description can point to this page. However I don’t see how it’ll make it more worse, it can ONLY get better - they’re either the same (in which case SPF will fail in any scenarios described here) or it’ll improve deliverability.