[O] Is it possible to delay org-babel fontification if the source block isn't visible?

[Oleh]

Hi all,

I'm using (setq org-src-fontify-natively t) with a file of about 100
source blocks in different languages.
And I'm getting a delay of 1-2s when opening this file.
I'm sure that it's the fontification since when I turn it off, the
opening time is fine.
This file has #+STARTUP: folded, so I'm thinking that there could be
an optimization
that fontifies a source block only when it's visible.
Is this feasible/already implemented?

regards,
Oleh