Yes, I think being able to submit the customs value in the order currency would be an extremely important feature, as it shows the transaction value most accurately and takes out an annoying manual step in label generation, as you have to manually calculate the correct base currency value for each shipment. Other providers have no problem in showing the transaction currency instead of base currency in customs documents (e.g. starshiptit royal mail click & drop, ...)
I agree this would be a very valuable feature. We currently sell globally in USD and EUR, in order to get the full benefit of the platform we would benefit massively from this addition.