Are there two slightly different discussions happening here?
There is a wide range of play activity which is encompassed in 'roleplaying game' - as noted, that could run almost from roleplaying-only collaborative fiction-writing in forum games to I guess something as game-only as Gloomhaven. Thinking about the many very different things that go into engaging in playing different games is worthwhile as designers can learn from each other, players can identify things they enjoy doing more than others and play games which focus on those aspects, etc.
But what might be interesting about trying to emulate the different ways of playing M:tG is the way that WotC overtly or tacitly provides support for different approaches in that game, but it's much less explicit in D&D: there isn't anything written into the rulebooks to help (for example) asynchronous forum play, speeds and spell-ranges are written with in-world distances which lend themselves to precise measurement rather than fast/loose approaches, monsters are designed to fit into the assumed approaches to play, and even the long-rest mechanic suits some types of game more than others. And so on. A product which was directly aimed at 'playing D&D in one-hour blocks' or 'playing D&D with the under 8s' could benefit from some different approaches.
Maybe that could be things that are as simple as 'here's a list of monsters at each CR which are quicker and easier to run, and don't rely on particular tactics or understanding complex mechanics in order to fulfil their role in a fun fight, which makes them great if you're trying to run two quick combats and some interaction in 55 minutes.' Or 'we've designed these spells in particular to be quick to run. It's probably best not to cast time stop and agonise over everything you could do with your extra time if you're trying to finish an adventure in an hour or two. Consider casting Power Word Kill (and, DMs, consider just telling players which enemies have below 100hp)'. But there could be direct mechanical things too, like a named mode of play where initiative is 'highest modifier goes first, play goes clockwise around the table', monsters always do static average damage, no-one uses spells or features which interrupt other turns, and so on.
It's interesting to hear that the new starter set will have a card-based character creation process they're calling 'the quickest way to start playing except for being given a pre-gen.' That's the kind of thing that it would be worth WotC innovating on, based on what they know about the different ways in which people want to interact with the game and its rules.
