The system in which you develop detailed documentation about the requirements, then create the software, and later let the users get their first look at it – and then, usually, get complaints that "it's just what I asked for, but not what I want" – is called the waterfall model. Waterfall approaches are not normally used by the WMF devs, as they're more suitable for projects with specific, limited, easily described objectives (e.g., software to control a machine on a factory floor).
Instead, the plan is to create something reasonable, to let interested people try it, and then to adjust based upon their feedback. This approach is generally called agile software development. This approach usually works well for our diverse environment of largely non-technical stakeholders, because different users can try it at different points and give their feedback, based upon actual attempts to use the software for real work, rather than having to find a bunch of people who can and will sit down and think carefully through every step of what they do and what they want and write down their requirements.
If editors dislike the initial state, then it's not really "wasted work". First, the goal is to get a few people testing it early enough, so that very little time and effort could be "wasted", even if every bit of it needed to be scrapped. Second, much of the coding work may be applicable to the next iteration. (For example: Imagine that the first copy-paste approach keeps bold and italics but discards links. There's very little "wasted" if editors then say that they want links kept, too.) And third, conclusively demonstrating that "X" is not the best approach is a desirable outcome.
 This particular project has been announced since at least 2013, mentioned at three Wikimanias and multiple Hackathons, described in e-mail messages, listed in Phabricator, named as a quarterly goal, chatted about informally for years, etc. From what I gather about discussions (e.g., at in-person events), the only questions that truly interest editors are:
- "Will I have to use this?" (Answer: No – or, at least, not for years and years), and
- "Will it just be plain old wikitext, and the wikitext on the screen is the wikitext that gets saved?" (Answer: Yes, that's how a wikitext editor works).
Beyond that, nobody really cares. From their POV, this is basically backend work, and of no more interest than the previous several times that the color of the editing toolbar was changed.