This is certainly possible. I only do not see the advantage in doing so, only a problem: This representation would directly reflect the internal data structure, therefore it could change quite often, even in the stable series. That means that this internal data structure should not be used by any other program.
Since we do not expect any other application to paste in lyx-internal format. Providing lyx-internal and pure text should be enough.
We would even need to make it versioned,
We can easily set format names to something like lyx-table-1.5.2 and prevent copy/paste between lyx instances of different versions.
I don't think that we should use the external clipboard for copy/paste internal to LyX, because IMHO the advantages do not outweigh the costs.
We somehow agreed upon many things. This has been encouraging. You know, I was afraid that people just like the current clipboard behaviors and would denounce any change. :-) Bo