Aside from who you're backing and the fact you're using BTC, which I agree might make sense in a classic risk/reward scenario, you're also betting on the website still being there in 4 years, though, which might be the bet with the biggest odds !
That is definitely one of the greatest risks. In the cryptocurrency sector, very few of the gambling sites and exchanges have that much lifespan. So if you are making a bet, which will be decided only in 2024, there is a real chance that the website will go down before that and you will lose your coins. I have never made any bets, which makes me to wait for more than three months.
You're right, but the price of the crypto used for the bet, is also an issue, if it fails during the period, you'll get coins that worth nothing in 4 years.