Spotted an interesting one earlier: I was passed by a muggle-looking cyclist (flat pedals, civvy shoes, hi-vis jacket under rucksack, waterproof trousers) going well on some kind of hybrid. Then I spotted the belt drive and gave it a bit more effort to try to satisfy my curiosity.... Large grey rear hub that I didn't recognise as a Rohloff, Alfine or Nexus, but might have passed for an older NuVinci if you squint (it was bigger and less shiny than the Sturmey-Archer hubs). There was a black bottle in the one cage on the downtube, so if that was a battery, it was a fairly stealth one. Just the two brake cables at the handlebars, didn't spot an obvious eBike console (though I only caught up for a second at some traffic lights before we went different ways, so didn't get a good look at the controls).
My gut instinct says some sort of stealth-ninja e-bike, in which case kudos to the manufacturer for commuter-oriented minimalism.