@fred4u, thanks for your comments.
I guess a schematic or a substantial part of it is copyright protected but I don’t think a redrawn collection of symbols would be (I’m referring to the many Helvetica or Times look-alike fonts that exist).
If you look at European tube and early transistor schematics from the 1960s then you might find that style not that uncommon (thicker envelopes and metric sizes), and it actually looks more like Elektuur started using similar symbols like some manufacturers’ application notes, repair schematics or handbooks did (except maybe for the Zener diode but there is also an alternative symbol).
I’m clear that they cannot be part of KiCad’s official release because of the KiCad-specific library rules (KLC) but I would guess it should be possible as 3rd party library?