I don't think people expect you to create a ui system as complex as css and html.
What most want, from my pov, is just having an easier time creating buttons, sliders etc. At least that would be enough for a start and could be expanded upon later, just how almost all addtions to the engines are done.
ProUI which was the gold standart ui tool for c3 (until Aekiro stopped supporting it) does not add any crazy complex layouting features, the only thing that gets close to any layouting is a basic grid of elements. The main thing it adds is a simple way to create buttons, sliders, radio groups etc.
While consoles supporting HTML5 would be a hugely amazing situation for Construct and developers using the engine, it's not really within our control, so is hardly a solution at all.
Anyone developing a game that might even only have a smitch of a chance to maybe be ported to console will not use html and css, which is a lot of projects.