Many emulsions of the past contained ingredients that can no longer be used due to envirionmental concerns. Add to that, with changes in basic materials like gelatin, you'd almost have to redevelop even an old emulsion like, say, Panatomic-X (if you just followed the last working formula, you'd get a film, but no idea what the speed would be until after it was coated, cut, and tested). Then the fact that *no company* has previously sold a designer-grain film slower than ISO 100.
"It's more difficult than we originally thought" probably means exactly that -- they ran into a snag of some sort, maybe as simple as getting a delta grain to grow small enough for ISO 25; maybe as complex as having to start over to match the response curve with the different sensitizing dyes (or lack thereof) in the slower emulsion. Doesn't mean they won't go ahead -- means they have to factor in the extra costs of developing the emulsion when they make the decision.
Honestly, I'm not a big fan of slow films, and in any case I can get all the slow film I'm likely to want (J&C sells three different microfilm stocks in 35mm cassettes now -- four, if you count Gigabit -- though no one offers them in 120). I'm not even a significant Ilford user, because my budget pretty much necessitates using the cheapest film I can find (which, fortunately, is still quite good stuff). I think it's very encouraging just to have Ilford considering developing and producing a new product in this market -- even if it doesn't fly, they've pretty well demonstrated they're listening to their customers and trying to make what we want to buy.
