How would these Ticket To Ride variants change the game?
I wouldn't say they're terrible ideas. I REALLY like the first one as it would add another layer of depth to the game. The second I personally would leave out, just because racing to get the train cards you need is part of the fun. Being able to cut other players off too easily could change things. The penalty would need to be pretty hefty, because you could easily rob somebody of 20 points as they try to complete a long route.

There's usually a few routes that end up critical to certain people in the game, and I could see a mechanic of "find out what destinations you opponents are trying to get to and do everything you can to stop them," which could make it a competition to see who has the highest negative score since nobody could complete their destinations. When you have to claim routes normally, you are loosing the privilege and resources to do something that would benefit you, and you need to have the right cards at the right time. Unless you happen to have a lot of cards or have been gathering cards of the same color by chance, you can't block. With contracts you'd be able to stop anyone at any time during your turn at the expense of just a few points if you didn't follow through later. 

In the original Ticket to Ride there's a powerful connection of short routes down the center of the country that link almost everything together. You could easily contract as many of these as possible in the beginning, work on your own destinations, then 'complete' your contracts at the end of the game since they're all short colorless routes.



I've found hardcore players have shot down almost many variations I've seen posted, such as drawing 3 cards per turn, having the option to build AND draw in a turn, having 7 cards face up the whole game, etc. See a list of those here. The game is very carefully balanced in the sense of East vs. West, long vs. short routes, and attack vs. defense. This doesn't mean variants are bad, and if you have any revisions or others I'd love to see them. It just means that there is a delicate balance you have to be careful not to destroy if you want the game to retain its original feel.

I haven't found many actual variants to the gameplay, but if you are able to print them and the additional cards there's a TON of fan created maps that give the game a new feel.

and there's always the catapult expansion...