If I recall an obscure reference correctly, it was ill-adviced that the Mindy teleporter be used through stealth/sensor blocked areas since it could scramble you on arrival or you'd teleport into something and be dead.
If you're looking for the rationale of "Why did the Mark 4 not have it before, and why could it have it now", it could simply be that R&D chose not to give the Mindy IV the full-featured stealth capabilities to increase the teleporter's efficacity. It could be that the teleporter tech has been refined enough since then to afford the Mindy IV a stronger stealth package.
Considering the availability of thermoptic camouflage on unarmored nekos and past Mindy models, I struggle to see why the Mindy IV would need an exclusive variant for it. Just implement said change, alter the letter at the end of the model number, and done.
Wes had a concern over it being overpowered... but this really isn't a new precedent in armor stealth. Nothing is being broken except the oversight that the Mindy IV should have probably already added this. Also, I actually think Ametheliana's listed caveats make sense and concretize how a Mindy IV can run silent.
Andrew evidently believes the Mindy IV is such a workhorse in a navy of small vessels with limited cargo room that they'd go for something multi-purpose, reinforcing my assertion that a special variant is not needed. His proposal is a nice peace offering to SirSkully, but thermoptic stealth is... just so trivial to Yamatai. Making it a modular add-on feels like it would just untrivialize it... which feels wierd to me.
I get the distress SirSkully could have over this, but experience tells me this is normal. The TARSA wouldn't be the first niche suit of armor. Jake and I both made the Sylph and the Harpy; both were niche unpowered models to the Mindy, and they only worked when the GM wanted to showcase them. Otherwise, they fell to the wayside really hard. The Daisy probably should have shared the safe fate, though it didn't, which is something I'm at a loss to explain even today. I'm not unsympathetic about the TARSA, but this predicament was bound to happen.
I've made most of my arguments. It's up to the steward to make his ruling (which I feel he already has, and I intend to respect that... but at the same time I was tagged, and I can be transparent with my opinion without meaning to be a dissenting voice).