Sandy, HP5+ isn't changing. Steve's point was that there's a new processing brew in the works that may alter its characteristics in a way that's useful for alt-process fans. Time will tell.
Ilford used to offer Delta 400 in standard sheet sizes, but sales of HP5+ were far greater, and so it was eventually discontinued. Delta 100 is the only Delta film offered in any sheet sizes now. Simon Galley can give us the official story, but at this point, I'm sure their reasoning is that bringing back Delta 400 wouldn't increase overall sales nearly enough to pay back the decrease in sales of HP5+ as well as the cost of tooling back up to coat Delta 400 on sheet film base (which they no longer do) as well as the cost of additional inventory as well as the administrative overhead of maintaining more SKUs.
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