Thanks for sharing Watno. Rebuild is really the only card I just dislike in the Dominion universe. While there are cards that I'm not a big fan of, I appreciate them and play with them. I was so close to house rule this card, but didn't do it because I don't like house rules in general. Now, that Donald X. himself admitted that this isn't really balanced I'm really inclined to house rule it.
1.) Well, some suggested to make it cost $6. At first I thought this is a valid move, but later I realised that it probably makes Rebuild games only worse because the strength of the card is the same and if someone gets a lucky $6 after the first reshuffle and your opponent not, he's maybe already miles ahead. So, it probably only adds variance and luck, that's not want I want to do.
2.) So, it was clear to me that the card itself has to be fixed, not the cost. But I really don't want a totally different card, like the one Donald X. suggested. The only thing I came up with is removing the +1 Action because, honestly, the +1 Action barely matters, but it can matter. I guess, it may add variance if you get Rebuild collision, but I think that's a good thing here, because you maybe want to add some support, Walled Village comes to my mind here, it would be great in a straight up Rebuild game. Because one thing I dislike about Rebuild is that it is rarely a bad addition to your deck, you can even add it in your engine and play it for great effect. Then the +1 Action matters. Also it matters with strong attacks which are usually terminal. Let's assume a Sea Hag board with Rebuild. It's a no brainer to add Rebuild to your deck, no matter if you go for Sea Hag or not. But without the +1 Action, you have to think twice, especially if you want to open Sea Hag.
3.) shark_bait's suggestion though I like maybe even better. Returning to the supply instead of trashing gives any other strategy more time and potential to catch up by grabbing a couple of Duchies in the end game. Also you can't force a game end by trashing Province into Province. Rebuild though may be a totally different card, but I'm eager to try it out.