I don't reallllly want to replace it because the risk seems so small... but will probably end up doing so.
Did you guys replace your supermicro motherboards?
Who else makes good server mobos?
That said, supply chain attacks have always been an issue and it's entirely possible that Super Micro has been a victim at some point. However, this will also be true of virtually any other supplier.
[1] https://twitter.com/marcan42/status/1049687546945392640
[2] https://twitter.com/riskybusiness/status/1049429881031819264
[3] https://www.servethehome.com/yossi-appleboum-disagrees-bloom...
[4] https://techcrunch.com/2018/10/08/apple-rebuff-bloomberg-let...
[5] https://www.businessinsider.com/security-community-voicing-i...
I wouldn't worry, I think the hardware attack described was pretty specific to that hardware. I am assuming that different super micro hardware would require a different hardware attack.
If china can get into the super micro supply chain they can probably just nip down the road and do the same thing for hynx or asus or whoever. So even if its true you are going to have a hard time finding decent hardware that isn't made in china.