Will we get more purchases on GOG instead of Steam? Or Steam users will not see any difference?

Here is the Steam's announcment:

https://steamcommunity.com/games/593110/announcements/detail/1301948399254001159

But honestly this personally wont affect me much since I use either GOG or Humble for gifting but certainly will hurt people who buy low,sell high.

I have no idea how STEAM does/did gifting, so I don't understand how it's different from buying a key when its price is low and selling it for slightly more?

Let's say I want to gift you Skyrim....

Will Steam seriously refund you if a gift that you bought, say, 3 months, ago is declined? Will the refund be in cash, or in Steam wallet?

I would imagine to Steam wallet.

This move is clearly intended to kill the reselling of gifts on G2A and the like. There's a lot of whine and cry because people liked to make profit from reselling games but for normal consumers I doubt they'll notice much difference. It's not like you can't gift games anymore.

The only thing I think they should still implement is a way to pay premium price for gifts if you live in lower price countries so it still allows you to gift games to people outside of your region, pretty much like GOG changed it so you can only gift games at premium price a while ago.

So would I, but some clarification (along with whether it's possible to get a cash refund in the first 14 days) would be nice.

It's not premium price. You can gift GOG games at US price or your regional price (whichever is higher) which is imho the best compromise compared to region locks and other crap.

At the bottom of the announcement:
Note: Pre-existing gifts will be unaffected by this change.
so the answer is no.

I was talking about a gift that you would buy after the change was made.

For those who keep games for trade purposes and all that's a direct hit. But there are also some maniacs (;P) and all who keep games in their inventory just to, well, keep them.
It's like a new way of storing games sealed - daf*q?!- and all in the craziest sense possible.

In that case I would imagine that the gifting period is unlimited, because as far as I understand it, it all happens internally on their servers, the client no longer has to deal with keys or inventory items.

Financial transactions are usually finalized within one month, so I'm not sure if Valve would want to receive the chargeback fee that would occur with the refund of real cash. No such issues with refunding to the Steam wallet.

Without a doubt it will be to Steam wallet.

I wouldn't expect much change on GOG's end. People are too stuck in the Steam ecosystem to really move elsewhere, plus GOG still doesn't have (afaik) a vast majority of Steam's (good) games.

BUT I could be wrong. Perhaps now G2A becomes all GOG keys.