There are plenty of unthemed rides that you can theme up yourself or check the workshop for rides we already have that have been pirated up if you aren't a builder.
As a builder prethemed rides really, really suck because you have to completely hide them, especially if you are doing a unique theme that Frontier hasn't added anything for.
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But what he is asking for is impossible at the moment. There is no way for anyone except Frontier devs to make a new flat ride from scratch that peeps can ride. And there is zero indication of any future ride packs at this time. There is no way for users/players to make pirate boat cars that animate and peeps sit in them. TMTK can't make working rides.