With regard to your addendum, while “Test builds” may be doing the good mapping, most folks I know aren’t using test builds, they may in fact be using significantly older builds (even when browser vendors push their updates – sometimes those updates get blocked by “Corporate”, as I know only too well first hand).

For this reason there is no harm, and some potential benefit to be had, by doubling up <main role=”main”> for the immediate future. Small price to pay I would argue.

My WebbIE web browser does some heuristics on the rendered page to work out the likely start of the content of interest and crops pages to show only that text. I can chuck “has a main element” into the mix. That’s good.

Of course, only a few sites will use it, and many will misuse it. But still progress to see real useful semantic elements.