FoIA is seldom of much use to me - its wheels grind very slowly (often far too slowly for me to meet deadlines), and I have to admit that it goes against the grain to deliberately tie up scarce resources, by imposing a long and bureaucratic process on people who have better things to do.
In this case, a FoIA request would involve Main Building civil servants, the IPT, and probably 41(R) is unnecessary paperwork to answer what is in essence a trivial question.
Were I asking about parametrics, tactics or for detailed information about the kind of capabilities that underpin these programmes (those things that might come under the heading of 'legitimate military security) then the 'need to know' reaction would be appropriate, and I'd be a clot if I didn't go through 'proper channels', and I would not want to 'push the boundaries'.
But the bare fact as to whether or not an announced programme, whose contract award was marked by the usual press releases, has been kicked into the long grass is not a military secret, and the only reason for hiding it would be to prevent political embarrassment. Since I'm not a civil servant nor a serviceman, I don't care about the latter.
In the case of TARDIS, my question has been answered by PMs, and in one reply my attention was drawn to a piece of openly released and publicly available information (that my efforts had hitherto failed to uncover) which answered that part of the query.
TARDIS is currently being rolled out fleet wide.
My question on PPRuNe prompted someone to draw my attention to a public source answer. No rules or regs have been breached, and a journo has learned that a good news story is still good news. Not only that, but we've saved hours of time and a small hillock of paperwork. That's money saved from the defence budget, too, so it's win-win!
In the case of TREV and ARTS, I still don't know the current status, but my suspicions seem to be widely shared.