Sufficiently advanced fantasy is indistinguishable from SF?

[Lusankya]

There's also Final Fantasy, where you have huge magic-controlled airships, electricity from magical sources, magic spaceships (sometimes), magically-infused guns and so on and so forth.

[SAMAS]

Well, there's always going to be the question of Technology. That is to say, what the civilization's level of technology was before it switched to Magic.

That's an unusual method of thinking. In, say, Lord of the Rings or Earthsea, magic is essential to the fabric of the universe, and it is highly unlikely that any civilization in either 'switched' to magic. Magic was always there and the society developed with it. Very few fantasy worlds are about magic just dropping in one day.

It's not "dropping in" so much as it is "transition." Example, the transition from the discovery of electricity to the point where it widely replaced gas lighting.

Likewise, there's going to be a transition from mankind(or whatever race in question) first discovering and working out the secrets of magic to magic becoming a driving force for their civilization. Depending on the level and saturation of magic as mentioned in a previous post of mine, the civilization's level of technology up to that point is likely going to be their jumping-off point.

[Gunhead]

Speaking of funky magical tech, Deadlands. It has weird science made possible by ghostrock, which both gives materials new properties and works as an energy source for all sorts of wacky inventions. Same goes for Warhammer Fantasy where warp stone does similar things, even if warp stone powered gadgets are mostly limited to the skaven. This type of magic powered engineering is what really blurs the line between real science and magic. Depending on the power output, it's easy to go from small gadgets to full blown steampunk to Steam Dreadnoughts in SPAAAAACE!
I think it's a shame magic engineering without fireball slinging wizards is a rare beast, maybe they're needed to make magic more magicky. Of course this touches upon another magic sub type, alchemy, which also mixes and matches magic and science.

-Gunhead

[Marcus Aurelius]

I call them mechanistic because they are predictable in their effects. In LOTR, you speak the password to a Dwarven door and it will open. Speak a spell of fire aloud and you can set a pinecone alight. Earthsea is the same way, but with true names instead. A non-mechanistic magic cannot be called a system at all, and would be native to a remote and alien universe and/or set of assumptions. You could write a story like that, or incorporate something like it into a larger setting (Mieville's Torque from his Bas-lag novels is probably the closest that I'm familiar with), but such stories don't really make up a meaningful percentage of fantasy.

I think you are cherry-picking a little here. There for sure is some predictability in LotR and Earthsee magic, but also a lot of unexplained things. Like in LotR magical abilities are greater in same races and again in some individuals of the races, but there is never any real explanation to that, other than they were created so, which is not really an explanation at all. Is it genetic somehow? Perhaps, but we don't really know. There are also evil places like Caradhras. It is predictably evil for sure, but why is that? Earthsea also has the "feminine" earth magic, which the wizards considered evil (in a classical patriotic fashion) that is bound to certain places in a very mystical way. Magical ability also manifests in some persons, but not in others, and it's even possible to lose one's abilities completely, but it's not really predictable why it should happen.