I still think generals.io is one of the best. There remain significant technical challenges to making HTML5 games at web scale. Making sure actual humans, not bots, are playing is of primary importance. Then there are the actual economics. Cloud traffic can become expensive even at <1000 concurrent players. Majority of revenue will be ad-based. There is demand for great browser based games. Even in LAN configuration. It's a question of who can invest in the web. And who can design specifically for the medium. With the result possibly looking quite different than 60fps arcade style games. Best of luck ;)