Would there be any inherent downside to using the Arches Platine for a traditional intaglio printing? Both the vibrant white color and more importantly the rich smooth texture is what I am after and it seems to have both.

There should be no problem printing the Arches Platine intaglio. The grade may have slightly more surface sizing than a Rives BFK or a Somerset Satin, but it should not affect the paper's ability to take ink from the plate.

The only other difference is that the Arches Platine is not buffered with Calcium Carbonate as an added benefit with reference to archival longevity.
You should take a piece for a test drive before investing in the print run to ensure the paper performs well.

"The proof is in the proofing"