Getting Around the Cross-Region Gifting Problem

Well, you can make your giveaways region locked, to ensure the winner is capable of receiving your gift.

I don't think the random winner can be trusted. He can just use the gift card to buy his preferred games rather than what he won from you unless of course you trust everyone entering in the giveaway.

I guess you can but you need to screenshot every step and conversation if winner will be dishonest.

Were there changes to region locks? I though NA/EU regions can gift worldwide

That's definitely a good workaround, but while it works quite well in small private groups/whitelists, public giveaways/groups are a totally different matter.
Another method would be to get help from a middleman (Poland is between EU and USA prices and can usually gift to both, save for weird exchange rate spikes), but it became a bit more difficult since Paypal raised their fees.
A third, uncommon method (with a bit of loss involved), is to have the winner list a unique or rare item on the community market, and buy that.

In the end, all of these methods require a certain level of trust between the giftee and gifter, which is a shot in the dark in a public environment.

How about fill his wallet? Cards have taxes