Even as retcons go, that's a pretty huge stretch.[..]Essentially the concept of the UT didn't exist until TNG.
But once the retcon is said and done, it dovetails perfectly to TOS. DS9 gives us explicit ear implants (for the Ferengi, but the technique would be sound). VOY shows us that after the removal of commbadges and other external devices, aliens who should have no business knowing English (the Kazon and Neelix - Kes is admittedly a quick learner) continue to be perfectly understood by our English-speaking (?) heroes, but the acquisition of a new language becomes impossible. And ENT brackets this with stories involving an external UT and others involving translations achieved without such. Kirk having an implant is a good "out" here, especially as implanted IT devices of all sorts are likely to be exceedingly common and expected by the audiences of today and tomorrow...