Ehh, I'm not a huge fan of this idea. You can already gift skins, and it basically does allow for abuse of the crafting system or for abuse of sales to gift friends skins.
Right now, you can't gift friends any skin shards you have in crafting or any skins that are on sale for the sale price. If you try to gift a friend a skin when it's on sale, you'll give it to them for full price to you. With this idea, you could buy it for yourself at half price, then trade it to a friend at full price, and you can also trade skins unlocked through crafting. There would have to be some kind of limiter, because on most skins, Riot gets a fraction of the cost on it if you got it through crafting, and that's assuming you actually bought the chests to get the orange essence/reroll, and sale skins are half price. The main issue is cost. Most extreme scenario is I have Spirit Guard Udyr, which I got from Hextech Crafting, and my brother got mystery gifted Pulsefire Ezreal. If he's an Udyr player, and I'm an Ezreal player, I could trade him Spirit Guard Udyr for Pulsefire Ezreal and we both get Ultimate skins we wanted literally for the cost of his friend's mystery gift. Crafting balances out by the random factor. For every Spirit Guard Udyr reroll that happens, there's hundreds of thousands of 520 RP rerolls, which balance it out because you actually spend more RP buying chests and keys than you do on 520 skins.