Yes, makes a ton of sense, thank you :)

BTW Doesn't ParametersAcceptorSelector::hasAcceptorTemplateOrConditionalType() need updating for all late-resolvable types? I'm not sure... (It's an optimization so that this block of code isn't called and some time is saved by not getting the arg types):

		foreach ($args as $i => $arg) {
			$type = $scope->getType($arg->value);
			$index = $arg->name !== null ? $arg->name->toString() : $i;
			if ($arg->unpack) {
				$unpack = true;
				$types[$index] = $type->getIterableValueType();
			} else {
				$types[$index] = $type;
			}

It should be fine right now because value-of and key-of are not resolvable if they contain a template type which is already checked. For simplicity and future-proofing it could be changed to just look for LateResolvableType instead.

Alright, done: 38198f1