It would draw a very small audience.
How can you really have road tests on bikes? Let's face it, for all the bollocks magazines pad their content out with one race/audax/touring bike is pretty much the same as the next, they all use one of the three major groupsets and it boils down to whether the tester thinks one is stiffer/more comfortable/livelier than the next. Most of that's rubbish anyway because those attributes are mostly down to geometry and little else.
I gave up reading road tests in the magazines years ago when I found myself losing the will to live half way through.
I guess that's why Top Gear does so well - they don't do road tests, not seriously. They did the new Ford Fiesta a couple of seasons back, wherein Clarkson proved you could get a horses head in the back, and it would carry him and three marines off a landing craft up a beach. Hilarious.
To capture the Top Gear feel, you'd have to just muck about, and find presenters who bounced off each other the way they do.
A magazine programme about bikes might work, for a very small interested audience, but road tests would have to be a very small part of it I think. To get maximum viewers, you'd need an eclectic mix. I'd be interested in stuff about projects like Cyclemagic, or my recycling job with the trike, but I'd be fairly bored by racing, whereas a great many people would be exactly the opposite. I think cycling is a wider subject in that way, than motoring, and more subject to the whim of personal feeling, because cyclists are so in contact with their steeds.