The Olympic game is releasing this year, not next. But under the assumption that Mario Golf is being made, you yourself raise exactly why Nintendo may not have released it yet, so as to not cannibalize the sales of the Olympic crossover. So if Mario & Sonic is this year, Golf may be next. Especially because Nintendo is known to sit on games so as to fill otherwise barren release windows, with Mario Golf being a fairly typical filler game.
If 2020 comes and goes without the Golf game, or some other Camelot sports title, then something may be up. But I wouldn't break out the yarn and the thumbtacks until then.
This is one of Sabi's sources. They have an NoA contact.
I can't speak for how much was directly conveyed and how much was extrapolated, but the source has yet to be incorrect about anything (to my knowledge, at least), and has been right on multiple accounts. I wouldn't outright dismiss their claims. Having said that, anyone who feels the information less than credible is free to come to their own conclusions, but dismissing some parts while holding on to the NoA portion is, at that point, cherrypicking.
Obviously it's unfortunate that he didn't become playable, but I wasn't 100% positive he'd even regain his AT status back, frankly. Clearly he merited at least that, if not much more, but the same could've been said for Smash 4, when there had been a GS game just two years prior to the roster being decided, with Isaac being the most popular character circa Dark Dawn, and we got nothing.
The most depressing scenario for me is we'd just have to experience that again, which seemed possible.
Well then the implication is that 90% of that post is guesswork, which, for a proven source, is a bit illogical. That'd be an untenable ratio to maintain trust.