The M1 Air (silver) arrived this morning and I've spent an hour or so comparing it to my i3 and taking it apart.
My biggest concern right now is that the battery connector is in a different location on the two logic boards. This means in order to swap the logic board you
have to also swap the battery. That's obviously quite a bit more work but not at all impossible.
You can see the battery connectors more clearly in this picture.
If you look in the image above the i3 Air (Gold) has the battery connector near to the fan on the left hand side. The M1 Air has the battery connector on the right hand side.
The second issue that I found is that the speaker on the left hand side of the MacBooks (right speaker when in use) has a very slightly different connector position. I'm not sure whether this will be an issue but from what I could see the speakers might be incompatible. This could require one speaker to be swapped along with the logic board. It could then also be required to swap the audio boards so that they stay with the matching speaker. If you also notice on the i3 (picture below), the speaker has a slight cut out for the fan which the M1 speaker does not.
To summarise, I believe it is possible to swap the logic boards. However, it also requires swapping the batteries, right (when in use) speaker and most likely the audio board. It's also required to swap the Touch ID sensor, although that is the same for any Touch ID MacBook. This means that it
won't be possible to just swap the logic boards in the future by just buying a logic board. You would have to buy an M1 logic board, M1 battery, M1 right speaker and possibly an M1 audio board. Alternatively, you would have to buy a whole M1 Air as I have done. Whether this is worth the work will be for individuals to decide.
I haven't decided if I'm definitely going to go ahead with the swap yet. I have a couple of weeks to wait for parts for the M1 Air. I'm replacing the screen, trackpad, right speaker and top case of the M1 Air. Those are the parts that have been most damaged by liquid. It turns on and functions fine so I think once it has those new parts it will be 100% again. Until then, I'm going to use it as a Mac mini to ensure that it continues functioning correctly. Once the parts arrive I will make the decision about whether to swap the logic boards and everything else that is required.