The preferred method of removing remjet is with an air knife. As it has less risk of damaging the film.
The point of removing remjet before spooling is so people can process it in transport C-41 machines, such as the frontier.
Regardless of stability, Portra 400 has been an all rounder better performer in C-41 than 5219 500T. 5230 500T should be than 5219 im general but Portra will be the best.
Then there is the colour rendition and skin tones of Portra to boot.
I would rather people buy more Portra, as I think this would be the biggest shame of any product to lose, period.
I also think Eterna Vivid 500T would be the better ECN-2 film for high speed and scanning. Then there is also Reala 500D. These are available from Taobao pre spooled for those interested. Labs in China have been doing the ECN-2 for stills thing for a while.
These films also suffer from high intensity reciprocity failure iirc, which may pose problems in colour rendition for shooters who mixed available light with flash.
Im also unaware if 5219 has an antihalation layer in addition to the remjet layer (as itd be rendundancy in normal usage).
Which would be an issue for having it removed by alkali treatment prior to exposure. The other thing is introducing more impurities to the emulsion prior to exposure. It is preferential to do it post exposure.