One suggestion: save all previously-processed (on HTML5 export) images for faster later exports.
They could be stored like image-opt.png along image.png
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This would save to much time, 1-2 seconds per export O.o This are 100-200 seconds per day which means I need to work 3 minutes per day more... Nope never !
This are 12 hours per year :O
Just skip recompression if you want a fast export, then when you're doing a real publish do the standard recompression.