You are speculating. If Bitfury's next chip design is not compatible with the chained design of the existing chips, then it's not going to work chips/cards/minit planes etc. How about wait until Bitfury actually announce a new chip design before continuing with this type of discussion?
It's not entirely unreasonable.
He wants to know if he will be able to upgrade his existing miner with new daughterboards.
It's quite possible this could be the case if Bitfury uses the same hardware interface (pinouts), even if the chips are designed to work completely different.
You are of course right that there cannot be any guarantee of this at this time unless Bitfury himself commits to a future interface.
Are the BFL Monarch chips compatible with 1st gen BFL products? That's the first of the 2nd. generation announcements so far that I have seen. The answer of course is a resounding no. BFL have gone down the path of reduced chip count, with a lot more GH/s.
If it were me designing asic chips, my 2nd gen would be a drop in replacement for the 1st gen if my target market was the DIY board designers, that way you get the boards out there as fast a possible.
The main thing to remember, is chips designers learn from their 1st gen efforts, and could easily come up with a better way of doing things that breaks compatibility with their past offerings.
There is no reason to maintain compatibility if you have found a better way of doing something, just for the sake of keeping the same pcb designs.