One reason for your client crashing in big fights has been eliminated. That's literally it. It won't improve your FPS, it won't fix desync, it won't let you go less potato, it won't open up any new gameplay changes, it won't fix lag. It just means your client won't crash if it tries to use more than 4GB of RAM.
It's a good thing and I'm glad they are doing it, but there's a serious failure to manage expectations here on CCP's part.
it won't fix desync
As you mention desync: At least two times in the past (one in 2010 and the last one in 2017) desync (to be exact: position desync) was caused by a different precision when calculation collisions on the 32bit client compared to the 64bit server. This was fixed by somehow forcing to use a lower precision (if I can remember correctly).
I am not aware, that there are any desync cases still caused by the difference of 32bit and 64bit calculations, but it is for sure a possibility. Unfortunately we could confirm a tiny bit of position desync in one of the 64bit mass tests (but in this case it was too little to be noticed without dev commands), so we can be sure that there are still other reasons around.
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