I think USDT is the only good other option because the markets are pretty hectic right now and a stable coin would be a perfect option. However most likely it won't be added because many people refrain from adding USDT due to regulations with the US federal reserve. The idea is that if they accept USDT, which is essentially US dollars then they will get some type of investigation. Believe me I tried to get lots of casinos to accept USDT and most refuse to list it.
XRP and DOGE are good but they are not good for long term holding. Pull up a chart for both and see how volatile they are. So sure they got transactions which are very cheap and fast however look at the price change over-time. BTC at least is more stable. Another issue with DOGE is that since its currently trading at 28 sats, if you want to buy it you will get a spread of 1 satoshi. And 1 satoshi doesn't sound like much but it makes a difference when the price is only 28 sats. So automatically you are losing 3.5% just on the spread alone not taking into account trading fees. So since BTC transaction fees are still reasonable now, most people just stick with BTC currently or ETH.