Personally, something that I would like to see you write that you haven't written before is an action book. In most of the books you've written previously, there was a lot of killing, and some action, but there weren't really prolonged fights, except in special circumstances. This is mostly due to the characters you write being smart enough to realize that fighting isn't the best idea, generally being more inclined to talk things out, but I would still like to see something like that. The litRPG genre that was mentioned would be good for this, or a high fantasy, which you also haven't written much of (the first books of YA is the exception). Also, I don't know if you've heard of Xianxia... (Dead End had plenty of killing, but the reliance on guns and one hit kills made prolonged fights infeasable).
Standalone books seem like a good idea, just because you have more freedom in them. In your current multiverse, you can't just change some things, without violating things you've written before. In standalone's, however, you're starting with a blank slate, you can make whatever rules you want. The main way I think this could be used is a story involving the afterlife, heaven or hell, which you can't really do in the current multiverse due to the whole 'no one ever really dies' thing.
Standalone books seem like a good idea, just because you have more freedom in them. In your current multiverse, you can't just change some things, without violating things you've written before. In standalone's, however, you're starting with a blank slate, you can make whatever rules you want. The main way I think this could be used is a story involving the afterlife, heaven or hell, which you can't really do in the current multiverse due to the whole 'no one ever really dies' thing.