There's plenty to do with roomscale. One of the things I wanted to try is to have platforms floating in the air, connected with power cables and you could travel between them by using these cables.
Own engine indeed opens many possibilities but also requires lots of additional work. I wouldn't recommend it though. Unless there's some really specific thing to be done. But even then, it might be worth considering using an existing engine. Engines today are great because of the pipeline and tools. Making it much easier to get more people involved in a project.