Yes, I know that unsigned kexts will load from /S/L/E, however I'm drawing a distinction between unsigned kexts and kexts signed with an identified Developer Id which is not Apples. I do not believe that these will load from /S/L/E, I think that for them to load they must be in /Library/Extensions.
You are not right in thinking non-apple signed kexts will only be loaded from /Library/Extensions/. There is no problem in loading unsigned kexts and an alert is just that, an alert.
I would say that this is a distinct possibility for the long term. However I imagine that Apple will encourage developers to sign their kexts and have them loaded from /Library/Extensions.
If we do look ahead to 10.10 with your thinking, do you propose that any of the current apps being used with unsigned kexts will not be able to run because these kexts have not been updated with proper kext signing?