If one were trying to create a board that I would use, it would most likely have to have 25-mil square pins on 100-mil centers. If that were the case, it would not be physical problem to provide pads for, say, a capacitor in 0603 package at each pin, one to GND and one to Vcc. I don't see any need for such pads on every signal, but ... if one needed a pullup ... well, there's an opportunity ... and if one needed a rate-limiting cap ... Well, you see what I mean. The problem is board space.

No adapter I've seen so far, has used the space under the IC, which makes the most sense to me. There's only going to be one IC on such an adapter, and, on the underside ... well, what better place for the bypass members? One problem that jumps right out at me, though, is that there are then about 10 cm of trace length between the bypass members and the IC pin, unless one drills holes to shorten the tracks. A solid Vcc and GND plane, as you mentioned, Per, would mitigate this problem.

A single-pitch adapter, as might be suitable for the SiLabs 'f120/130 parts might be worth a try, and, if one were going to be that application-specific, perhaps a place for the oscillator and JTAG features wouldn't be a bad thing either.

Now, for my purposes, the goal would be to make the IC wire-wrap-board compatible. By that I mean a board with the matrix shown (I think) on my "personal web page" on 8052.COM, from which I've had to remove a considerable amount of information, as the amount of available space was reduced by about 75%. I don't know what objectives other potential users of such an adapter would have.

Perhaps you could shed some more light on your view?

RE