I agree: as long as side channel attacks are possible, there's always the possibility that someone else will find some other vulnerability that can be combined

I agree: as long as side channel attacks are possible, there's always the possibility that someone else will find some other vulnerability that can be combined to create an exploit. The paper (https://meltdownattack.com/meltdown.pdf https://meltdownattack.com/meltdown.pdf) does present it in that way: they show you the parts, then show how they fit together for a workable exploit.