This does concern me - especially as Mattel has already hinted that next year's vehicle may contain electronics.
I certainly wouldn't mind a sticker added to the item, but then I open everything anyway. But seriously, with enough advance warning you would think that Mattel would be able to sort this out. I've bought plenty of electronic toys from the States and had them shipped to the UK. The Star Wars Episode 1 Naboo Cruiser being the largest example. Most of the branded toys at retail over here are identical to the US releases. No actual change has needed to be made to the item.
In the short term, I can just go to eBay for anything that Matty won't ship. But it's not a reasonable solution. This will become especially problematic if electronic items are ever part of the subscription. What will happen then? Bar foreign subscription orders? Just leave out the electronic items?
This is definitely something that needs to be resolved.