Sorry, I was a bit annoyed and left this forum for a few days so I wouldn't write something nobody want's to read ^^°
I would rather introduce an eyecandy object, which may inherit from wayobj (the good things of OOP).
Isn't the best eyecandy object actually the ground_object? I mean, beside trees, that's the only object that has no function. Even citycars obstruct ways and therefore influence gameplay, but I don't think anyone builds around woods or groundobjects to save cash. And if it is an object to be placed on ways, it would simply be a way_object, even if you call it differently (because the "old" wayobject which is then probably no longer meant for eyecandy would be electrification. Although I understand that, for compatibility reasons, you can't change the name of those)
Another road-ish waytype has been proposed before, but no one wanted to implement it until someone could explain what they needed it for.
Aerial lift. Especially in paks with double height instead of half height, aerial lifts as elevated ways which can climb steep slopes might be interesting. However, they'd probably need additional rules to really work fine.
If crossed with tram, so that you can have both roadlike ways on the same tile, maybe an extra bike/horse lane? (but if copying the tram code was easy, it should be implemented in the other rails anyway)
Any kind of Sci-Fi vehicle might be bidirectional (and any pak can have sci-fi stuff in the future)
Any "national" pak of a nation that has no access to the sea might choose to use a second bidirectional way as channel for ships.
Footwalks. I mean, if you copy the road code, you can copy the citycar-code as well. If you then use people as vehicles of length 0 or 1, you could have more vivid cities. Or just manually place them as vehicles that have no graphic when empty, but look like people when occupied with one passenger, to even decide on the amount of people individually.
There are possible uses, so if it existed, I would definitely use it in some way or other. But none of these uses is really enough to require it, just a minor nice to have.