The slow apertures indicate to me a wish to sell Leica-quality lenses at lower prices. As there are already lenses at f/1 (50mm only), f/1.4 (35-50-75) and f/2 (35-50-75-90) there would be no sense in duplicating what already exists.
Most people use significantly faster films today as their everyday films than they did even 30 years ago, especially if they shoot colour: in 1967, Kodak's High Speed Ektachrome (160 ASA) was the fastest colour film available (Ansco 200 and 500 came later) and Kodachrome-X was the standard fast colour film. Many neg films were still 40 ASA.
What is more, anyone who wants fast film in their Leica today can get a lot more of it, and a lot faster. Royal-X Pan was never available in 35mm; HPS was never much of a success; and today's Delta 3200 is over twice as fast as 1967 Tri-X and a lot more suitable for pushing. In colour, even ISO 200 (probably the standard slow negative film today) is 2-1/3 stops faster than 40 ASA, allowing the same shutter speed at f/3.2 as you'd have had at f/1.4 in the early 70s. The same increase applies among the fast films: 800 is 2-1/3 stops faster than 160.
In other words, the heyday of the ultra-fast lens is over. There may be one or two more in the pipeline faster than f/1.4, but I doubt we'll see many. The Summarits are common-curve lenses, a lot cheaper to grind than aspherics, but the lower aperture allows easier correction.
Why f/2.5? Because Kobayashi-san has already established this for 35-50-75, and many might be swayed by the 1/3 stop. There are also 50/2.8 and 90/2.8 lenses in the current line-up (I think -- I've not checked lately) and the idea is to have a new series of lenses, all consistent. I'm surprised they didn't go for f/2.4, 1/6 stop faster than f/2.5 but on the half-stop rest, not 1/3 stop.
Before these lenses were announced, I was thinking of doing an article on how we may be clinging to the past with fast lenses when slower ones are smaller, lighter, cheaper and often better.
Of course the availability of ISO equivalent 2,500 on the M8 means that for colour, there is even less need for speed, but to describe these lenses as 'designed primarily for digital', let alone 'troubling', seems to me all but meaningless. After all, what would 'designed for digital' mean, that could have adverse implications for silver halide? Higher resolution? Closer to telecentric? There might conceivably be more vignetting, but I'd be astonished if that were the case with these focal lengths and apertures.