I think 2016 is a bit too early but yeah, xoofx first wrote about CoreCLR in 2018 and said he'd made considerable progress with something like himself and two other engineers doing it as a side project. That is four years before Unity as a company announced the migration as a priority, which in turn is another four years before the current estimate for when they may ship it.

From my perspective, Unity seems very poorly managed in recent years. The editor experience isn't improving while they continue the usual pattern of shipping features in a poor state where they need another couple versions to become properly usable, and of course they make terrible decisions like the runtime fee, a total insanity that caused a huge loss of trust and boosted Godot development enormously.

Of course my perspective is biased by me not being Unity's main target market. I work on PC strategy games, which are on Steam. At our studio, we don't do mobile, advanced graphics features aren't very relevant, and we may have the most complex UI that ever shipped in a Unity game.