I don’t know about wisdom, just memory. The Steyr entry in the US Army’s 1980s ACR competition fired a flechette round through CTA ammunition. This round had a lot of problems with robustness of the case and stability of the flechette (sabot release, etc) so very much underperformed. On paper it was pretty lethal with a muzzle velocity of 1,450 ms that was retained through much of the flight. From memory it was still travelling at around 1,000 ms at 1km range. The use of CTA ammunition also enabled it to have an annular primer and a fixed, right angle firing pin. The action of the weapon was extremely simple and likely to be very robust in use.
The flechette used in the Steyr ACR was not a micro flechette it had a diameter of about 1-1.5mm so it would be quite easy to make in conventional castings or machining. Even made from such methods it would be highly effective at body armour penetration thanks to its velocity and sectional density. I guess single crystal super alloys could be a material for producing very strong small arms flechettes. But then you would have an infantry small arm able to penetrate tank armour!