So, something very similar to fitness trackers and smartwatches? As others have pointed out, no flexible power sources; realistically you're going to end up with a single SoC that already has bluetooth, such as the Nordic Semiconductor ones.

Most of these devices have on-demand displays to save power.

Miniturising it and making the casework function is the hard part. You might be able to build a "desktop" version of it fairly easily..