Services shut down and that’s why you don’t use them as your sole storage point. You don’t lose anything if they shut down that way :D You can still use them for the convenience of the people you work with.
In any case, it doesn’t sound like you’re anywhere near needing testers, you’ve still got a lot to think about re: level design. It’s challenging enough to design a fun platformer area without also making sure it works in 4 different ways without just sectioning off different parts of the map.
SotN is an interesting rare example of two-way level design, but I don’t think it’s a fantastic example overall. Some maps are done well and jumps work nicely (mostly these are the maps where it’s just 1-tile-thick platforms where it’s inevitable that jumps would work both ways), but a lot of the Inverted Castle is not like that, and it’s more about High-Jumping and Flying your way through. The maps that do work well don’t play significantly differently, and it’s the maps that don’t work very well that let you switch up how you navigate them. I think that’s something worth thinking about.
Although not actually similar to your idea, you may want to look into the maze needle subgenre of I Wanna Be The Guy fangames for inspiration. I’ve not seen any that employ level rotation, but some have level designs that are seemingly quite open, and the challenge is to find the correct path between all the platforms to the exit, with platforms that felt like an obstacle before becoming the path to the end later, or vice versa. I think this approach could lend itself to some very interesting levels, as the solutions for each rotation would be quite different, and the levels could be open enough that rotating the level wouldn’t leave you with just one obvious path to the end. If you need a starting place for your research into these games, try I wanna qoqoqo origin and the other games in the qoqoqo “series”.
Another not-entirely relevant game worth looking at is The Bridge, which is a puzzle game where you rotate the map while you navigate it. Although that’s very different from your goal, some of its levels do have areas that are navigated differently depending on which way they’re rotated, and might give you some ideas. The game also employs gravity as not only a way to keep levels solvable, but as part of its puzzles, as gravity works against you a lot of the time. (Incidentally, I actually rather dislike this game, in a large part because it spoils the perfectly good rotation mechanic with some additional mechanics that don’t work with it very intuitively.)
Earlier you mentioned doing square/rectangular levels. Don’t discount slopes or rounded shapes entirely! They can still work well even with rotations, and I feel that slopes are what made some of the inverted SotN levels feel fresher than they otherwise could have, even if it only felt like a nice touch rather than something that changed up the gameplay. 45 degree slopes work at any rotation with only very basic physics logic. Other slopes would be more complex, but could also be more interesting. That said, a game made up entirely of e.g. square tiles could still be very fun, so if slopes don’t appeal to you, don’t feel pressured to put them in.
NGL to me the biggest appeal of this project is “holy crap you can store each world as just one map and rotate it in-engine, that’s hella cool” :'D