I don't disagree with the OP comment, however I think this shouldn't be read as a change to immigration rules, only a different form of implementation (and the imposition of a small cost).
The '90 in 180'
rule has been in place for some time now (and applies to the majority, if not all, nationalities mentioned) but currently compliance can probably only be checked by inspecting passport stamps, whereas ETIAS, when implemented, will be a Schengen-wide electronic database so will flag up any overstay automatically.
Also, theoretically, ETIAS's bio-intelligence will be able to spot if someone is trying to use two passports (multiple-citizenship) to get around the rules.
Entry to the Schengen Area (and indeed most countries in the world) has always been subject to the whim of the immiigration officer on entry - so no change there.
My understanding is that pleasure vessels' crews are, and will continue to be, subject to the same (90 in 180) rules. However it's unlikely (in my opinion) that all
current 'Ports of Entry' will be equipped with the necessary
equipment to facilitate ETIAS by its implementation date (which, as was mentioned above, has been delayed multiple times already). The effect of this might be either to reduce the number of
Ports of Entry until the necessary upgrades are in place, or - hopefully - continued use of passport stamps in the interim.
Much more irritating for cruising sailors is the loss of non-Schengen countries in the EU area;
Croatia was a very helpful respite for a Schengen-shuffler until it joined the bloc at the beginning of this year. Hopefully
Turkey (now decades from EU
membership surely) won't decide to apply for the Schengen half-way house while it waits!