I was also confused, but from some Googling it looks like it's a phrase that's frequently been used in this particular fight, by supporters of the cycle-route plan, to ridicule opponents of the plan. Possibly okay to assume your reader would recognize the phrase if this were a London newspaper, but on Slashdot less likely.
The phrase "old men in limos" with acronym "OMILs" appears to have been coined by Chris Boardman, an Olympic cyclist, as a riposte to the term MAMIL, or "middle-aged man in lycra".
It was later picked up by Boris Johnson's administration, e.g. here's an article from June in which London's cycling commissioner says,
"It was at times nightmarishly difficult to manage this, and we saw some absolutely ferocious resistance, kicking and screaming, and we saw a lot more passive resistance, heel digging and foot dragging from whom Olympic cyclist Chris Boardman called Old Men in Limos; you've heard of the MAMILs, those were the OMILs. A lot of objections, which would nearly always start with the words 'Of course I support cycling...'"