Sorry, but I don't think you're right about the RAW.
Page 161 of the rulebook, under the spell description, specifically says that "the tunnel does not, of itself, grant any sense impressions of the target." Page 80 specifically says that "Hermetic magic cannot affect an unsensed target without an Arcane Connection".
The canonical spell is of Arcane Connection range, so of course the Limit of Arcane Connections doesn't limit it. It only becomes an issue if you try to get around the requirement for ACs, which the original designers wisely didn't attempt.
I think you are confusing actually touching a target through IT. The spell allows the use of touch range spells. It does not say that the caster touches the target. A mage can not grab the target of a IT nor punch or shoot an arrow through the tunnel. Perhaps, because of the metamagic, you touch the AC when casting the spell and it acts as a link to the target. The target is not touched.
This, of course, fails when thinking about the sight ranged IT. So perhaps the spell creates a link to the target so that when a mage is casting a spell they are touching the IT which provides the link to the target.
One might argue that the caster's Vim is touching the Target's Vim, since that's the Form involved in the spell. The lack of other forms means that the caster's Corpus, for example, can't touch the Target (as you say) and also presumably explains why sensory impressions can't travel by the IT.
Some connection must exist, similar in some ways to an Arcane Connection but different in other ways. Otherwise the metamagic would have to target each of the caster's spells, to extend their range from Touch/Voice/Sight to Arcane.