Far as I can tell, someone wrote:
install a hydrofoil to improve matters? What's the
downside? I am always skeptical about aftermarket devices like these
because you would think that a manufacturer would ofer them standard
or at least as an option if they meaningfully improved performance
with little downside.

I thought the same thing for a good while.

I used to ride a motorcycle back in the 80's.
To improve comfort, I bought a "Windjammer" fairing, which was a
windshield with "lowers" to protect the entire body from wind and rain.

http://www.xs11.com/tips/modifications/wjv.jpg

It worked very well. Only Harley (and maybe BMW) offered fairings.
Even the famous Honda Goldwing did not have one available from Honda
until years later. Now virtually ALL touring motorcycles come with
fairings standard.

Windjammer went out of business when motorcycles started making their
own.