I don't believe the will of Satoshi is particularly relevant on this matter. Having a term everybody can converge on to express small amounts is very important to improve the user experience, and satoshis seem to have more chances to achieve this than scientific notations.

My main concern with satoshis as a unit is that it may sound weird/funny to native Japanese speakers. It could probably be useful to have the opinion of some of them on this topic.

Regarding the BIP to formalise the symbol for satoshi, I think that maybe is better to wait for something to emerge with more widespread usage (e.g. already used by some wallets or service providers). The linked proposal does not seem to have sufficient support to be proposed as a standard.