Uhh, yuck. Although I can understand needing one (kind of) for Ignem.
I would be wary of using damage as a comparative example. I'd say specialising in teleportation is stronger than specialising in damage. Because, while damage can cover a wide variety of arts and forms, the effect remains singularly specific: you do damage to something (with an effect that uses the soak rules). That lets you get the benefit on a wide variety of spells, but those spells all do the same thing - you just get to kill people in a bunch of different ways. I'd actually say it's a very bad example of a major focus; while it looks versatile, it's really not. You could specialise in stone (another major focus example), get a wonderful variety of earth spells to play with, and be almost exactly as good at doing damage as the person who specialised in damage. Especially as the default "do damage using terram" spell is a Cr(Re)Te effect - automatically taking advantage of the focus.
I disagree that damage cannot be designed intentionally to be broader. At the very least the tools which damage can also add some utility. The moment a new thread starts with alternative uses for damage spells we will all see the uses.
A fire spell that burns so hot it can melt other things being used to melt through metal and stone walls? Or a creo and rego Terram spell to create a giant scoop or blade to strike with, but also excavate earth?
At this point I think the moderate view seems to be it is a Minor Magical Focus, given it should not include the edge cases - and yes, the implementation of teleportation spells in a saga and the troupe's view will always be variables.
If you avoid all the tricky and strange ways others are defining it, I would say Minor. So exclude Summoning and taking someone's heart or anything to do with spirits. Limit it to "safely moving yourself or someone else from one place to another instantly".
Watch as all the philosophers tear that apart...
I don't have a problem with the above in quotation definition being a minor focus. But keep it handy, preferably written right next to (teleportation) on the character sheet or it might start broadening with time.
It's all in the definition of "teleportation".
"Any of many (mostly hypothetical or fictional) processes of moving matter from one spatial point to another without physically crossing the space in between and which are often depicted or described as happening instantaneously, and through dematerialization or gateways." is a little more general and doesn't really seem tricky or strange.
This excludes teleporting things, which is probably really useful.
Hey, you want your magic useful, pay up for the Major Focus 
Eh, Major Magical Focus generally isn't worth it. When you have even a Minor Magical Focus, you put your efforts into using it as effectively as possible. You can do that a little better, but not nearly three times as well with a Major Magical Focus. For instance, look at what you can do with a Minor Magical Focus in canines or similar (or ghosts or similar if you can make a spirit a Familiar). You get a Familiar of the appropriate type. Now everything you do with the Familiar Bond gets the bonus in addition to all the other things you would normally use it for. If you neglect the familiar, just consider the multitude of things you can do with something like self-transformation.
It was way more worth considering as an investment before the Minor version's errata.
But that part of the errata is there because without it you could increase your Arts and have your casting total go down with a Minor Magical Focus. That seemed (and still seems to me) pretty nonsensical and not what was intended.
I'm not saying that made more sense, it's just what the Major version was originally balanced against, thus the explanation of why the improved Minor version isn't much worse than the Major now.
It was the thing it was balanced against? Only that? The Major version should have a breadth smaller than a single Art, and as Forms have less breadth than Techniques that should mean less breadth than a Form. Meanwhile the Minor version should have a breadth smaller than a TeFo combination. So the Major version can have five times the breadth of the Minor version. It's just that if you can manage to do 50% of everything you do via the Minor, there is no way you can pull off triple 50% with the Major. So, yes, the original way they worked was part of it, but having five times the breadth really has to count for something. Having five times the breadth of a Minor Virtue really should make it Major Virtue, it's just like that some like Secondary Insight aren't as good as other Major Hermetic Virtues.
An interesting possibility to consider for the minor version- a lot of ancient stories have tales of a magician taking their heart out and storing it somewhere else to keep it safe. What if you can teleport out someone's heart, but it doesn't kill them?
This sounds sooo like the Head of Vecna.