One license across both platforms would be great! I use both Windows and macOS for work, and switch between frequently.
Just to provide an example of how another company / application approached this problem:
I purchased the excellent 1password software by AgileBits from the Mac App Store. Their policy at the time was to give a 50% discount code for a Windows license if you emailed customer support and attached a copy of your Mac App Store receipt. I took advantage of this policy, and appreciated the discount.